• Bushings
• Castings
• Cold Forming Parts
• Custom Bolts
• Custom Fasteners
• Custom Rivets
• Custom Screws
• Forgings
• Plastic Injection Molded Parts
• Powdered Metal/Metal Injection
• Rubber Parts
• Screw Machined Products
• Springs
• Stampings & Fine Blankings
• Steel & Stainless Steel Balls
• Tubular Parts
• Wire-Form Parts

Castings or Forgings?

A Realistic Evaluation

An honest presentation of the advantages and limits of both steel component forms allows users to make informed choices when considering a forged or cast design.

Malcolm Blair and Raymond W. Monroe,

Steel Founders’ Society of America, Crystal Lake, Illinois

Much has been said and written recently by the forging industry about the advantages of forged products over castings. Such articles with headlines such as "Upgrade to Forgings" intend to imply that castings are in some way inferior and less reliable. It should be recognized that castings and forgings start from very similar beginnings and castings can have some very distinct advantages over other product forms, including forgings.

This ice cleat (for a U.S. tank application) illustrates the possibilities available through metal castings. Conversion from a forging to a design taking advantage of the casting process reduced the lead-time delivery by 70%.

The Process

Most steel components start as castings: metal that has been melted, poured into a mold and solidified. In the casting process at the foundry, because the mold has the shape of the desired component, all that remains to be done after casting are the various finishing operations.

With forgings, the first shape is an ingot or continuously cast billet. Ingots are large, usually rectangular in form and weigh up to several tons. Ingots or continuously cast billets are forged into shapes by hammers or presses. Extensive machining to final configuration usually is required, and welding also may be necessary before finishing operations can begin.

Table 1 shows typical casting and forging procedures for producing a 10-in. valve. Although no two foundries are identical, all would essentially follow the same procedures identified in Table 1.

Table 1. Step-By-Step Comparison of Producing a 10-in. Valve

For forging shops, however, two alternatives are possible: forging two halves and welding them together, or creating the internal channel from a solid billet by piercing and machining. Piercing consists of punching a hole through the piece. The hole then is tapered in shape, but may require extensive machining to bring it into tolerance.

Although there is a substantial area of overlap, forgings tend to be used exclusively in some applications and castings in others. In determining which process to select, the crucial considerations are the ability to satisfy the design criteria and the ultimate cost of the component.

Section Thickness/Shape

In forging, metal is moved while it is still in the solid state. Because the forging billet is solid, substantial force is required to change its shape to the desired configuration. Because of this, the required force increases as section size increases. In practical terms, there is a limit on size and section thicknesses produced by forging.

This doesn’t mean that very heavy sections are never forged. But when they are, relatively little deformation or reduction in cross-section occurs. In other words, the surface of the part merely is moved from one place to another.

In contrast, in the casting process the metal starts as a liquid and flows into the desired shape. Therefore, it is practical to cast components of large sizes and section thicknesses. For extremely large components, cast/weld construction is generally preferable to forged/weld construction. The reason is that fewer parts are typically involved, and because steel castings tend to have better weldability than steel forgings.

In forging, solid metal is forced into the die cavity. In casting, liquid metal is poured into the mold cavity. Liquids can flow almost anywhere. Therefore, as complexity of shape increases, the practicality of forging decreases. Castings can accommodate great complexity of shape.

Composition

The question of composition has two parts: what is obtainable from foundries and forging shops, and what is or isn’t castable or forgeable?

Forgings are produced from billets obtained from a steel mill and in compositions produced by the mill. Mills tend to produce limited grades of steel and special orders can be prohibitively expensive. Because steel foundries are more flexible, the number of chemical compositions obtainable from steel foundries is virtually unlimited.

Although a single foundry cannot supply every conceivable alloy, it is always possible to obtain a unique composition to meet a unique requirement from a variety of foundries at lower cost than competitive product forms.

The presence of controlled amounts of ferrite in certain stainless steels leads to increased corrosion resistance, higher crack resistance and better weldability. Ferrite occurs normally in most cast stainless steels, with the ferrite level controllable to produce the desired combination of characteristics. However, ferrite impairs hot working properties and is normally not present in forged components.

The important class of work-hardenable steels also are not forgeable. Work-hardenable steels are generally high-manganese (approximately 13% Mn) alloys that become harder the more they are worked. Thus, they are ideal for dipper teeth, compactor feet and other earth-moving and excavation applications.

Mechanical Characteristics

The principal mechanical properties of interest to designers are strength, ductility and hardness. But how does the user know the mechanical characteristics of a part?

For cast steel, it is relatively easy. If the component is made from a standard alloy, the characteristics are given in a standard specification. If it is made from any other alloy, standard foundry tests will provide the answers. The values will apply to that component regardless of the axis along which measurements were made.

Many metal parts are made from rolled products like bars or plates. The rolling process changes the properties of the metal. The major advantage is that the strength is increased in the rolling direction or the longitudinal axis. Both forgings and fabrications have directional properties as a result of the rolling process.

However, tensile strength, elongation and impact properties decrease in the transverse and axial directions. Thus, wrought steel and forgings in particular, are anisotropic (exhibiting different values of a property in different directions). For equivalent alloys, the ductility and impact strength of steel castings generally lie between the longitudinal and transverse values of forgings. In castings, the metal is isotropic, with similar properties in all directions (see Fig. 1–2).

Fig. 1. These graphs demonstrate the relation between the mechanical properties of rolled steel and the angle of inclination of the test specimen.

Fig. 2. This figure illustrates the influence of forging reduction on anisotropy for a 0.35% carbon wrought steel. Properties for a 0.35% carbon cast steel are shown in the graph by a star (*) for purposes of comparison.

With respect to the mechanical characteristics of a forging, most forging references provide only longitudinal characteristics. To obtain the transverse or axial characteristics, the user will probably have to request them specifically.

Additionally, the service conditions of the components must be carefully evaluated. If the loading is uni-axial along the longitudinal axis, then the directionality of the forging is an advantage. As the stresses increase in any other direction, directionality becomes a problem. Pressure vessels are good examples of applications where stresses are triaxial. The design code (ANSI B16.34) used by most flow control manufacturers doesn’t indicate that forged products offer any mechanical property advantage over cast products (Table 2).

Table 2. Tables 2-1.1 and 9 (ANSI B16.34

In terms of temperature extremes, corrosion resistance and wear resistance, "equivalent" castings and forgings generally perform equally well throughout the temperature range and are generally equally resistant to corrosion and wear. With regard to corrosion, however, cast stainless steels with controlled amounts of ferrite will probably be superior to their forged counterparts, since ferrite generally increases corrosion resistance. With regard to wear, work-hardenable steels can, for practical purposes, only be obtained as castings.

The Practical Purchaser

Design and Design Modifications—Although castings and forgings have many design criteria in common (the need for generous radii, for example), each has its own recommended practices. When changing from one process to the other, the design should be reconsidered and new drawings made, or problems are likely to be encountered.

Casting and Forging Defects

The modification of a design is a different matter. It is often necessary to alter a design by adding a rib or lug, removing a projection, etc. Here, castings provide a distinct advantage, since the modification of a casting pattern or corebox is relatively easy and inexpensive. But the modification of a forging die to accommodate even slight changes is usually difficult, very expensive and new dies may be necessary.

The manufacturing process also places limitations on the shapes that can be produced. Often, foundries must explain to customers that to induce directional solidification and enable the pattern to be removed from the mold, it is necessary to introduce a taper of about 1.5°. According to the Forging Handbook, this magnitude of taper is typically 5–10 times greater in forged products.

Fabrication—If two components are to be welded together, it is advantageous to have one or both parts be steel castings. Castings are generally more weldable than "equivalent" forgings. This is true not only of austenitic grades of stainless steel with controlled ferrite, but of plain carbon and low-alloy steels as well.

The superior weldability of steel castings was demonstrated in research performed by the Univ. of Tennessee. Five "equivalent" grades of low-alloy casting and forging steels were compared in terms of weldability, or resistance to cold cracking.

Cold (or underbead) cracking occurs after the welded joint has cooled. This can be extremely troublesome since cracks are hidden beneath the weld and aren’t revealed by surface inspection.

In the Univ. of Tennessee tests, cast and wrought grades of 8630 steel plus four other manganese-silicon (Mn-Si) grades were tested to determine the degree of preheating necessary to eliminate underbead cracking.

For each grade, the cast steel required lower preheat temperatures than the wrought steel to achieve crack-free performance. Baseline tests to establish the weldability of the grades without preheating showed the same results. Every cast grade was superior to its wrought "equivalent."

The problem with the wrought steels has been identified as the elongation of the inclusions. The needle-like inclusions in wrought steels appear to be more likely sites for crack initiation than the round inclusions in casting steels.

Where welding is required, the same considerations apply as previously mentioned. At a given preheat temperature, welds on steel castings tend to be less susceptible to under-bead cracking than welds on steel forgings. Additionally, castings will achieve comparable weld reliability at lower preheat temperatures.

Final Costs—The final cost of a part includes its purchase cost plus the cost of performing any necessary additional operations.

Before assembly operations, for example, it is often necessary to machine the part to the desired shape. This cost can be considerable. When parts are relatively simple, castings and forgings tend to require equal amounts of machining. As parts become more complex, however, castings tend to require less machining.

Upgrading—The forging process tends to reduce surface porosity and discontinuities (and may close up small internal cavities). Surface porosity and discontinuities occasionally appear on steel castings and require weld repair. The resultant surfaces meet the same standard requirements as the casting. The cost of this upgrading procedure is usually much less than the cost of additional machining typically required of forging.

Size and Weight—Steel castings are almost always lighter than their forged counterparts and the redesign from forgings to castings usually results in substantial weight savings. For example, a forged muzzle brake for a cannon anti-recoil system weighed more than 600 lb. The cast version weighed 400 lb and lasted more than three times longer.

Set-Up and Production Costs—The key to the casting process is the pattern. The key to the forging process is the die. Pattern costs are substantially lower than die costs and can be amortized over shorter runs. With higher runs and with simple component configurations, forged components can become economically converted to equivalent castings.

Castings will tend to have a definite advantage over forg-ings when any one of three conditions is met:

• a unique metal composition is required;
• the part is relatively large or complex;
• stresses may be multi-axial.

The Competition—How large is "large?" How complex is "complex?" When does a production run become "long?"

These are the gray areas in which neither castings nor forgings show a clear-cut superiority. The solution for the designer is to determine the method of production before finalizing the design. A preliminary design will allow the customer to take advantage of the competitive situation. Invite bids from reputable foundries and forging shops and decide which process to use on a specific, case-by-case basis. The results may vary in different cases, but the competition can only serve to benefit the customer, user or purchaser.

Ask the Producers

Clearly, steel castings have and will continue to maintain an important role in manufacturing. Their strength and ability to be produced to the shape required by designers should ensure that their competitive position will be maintained and improved.

Designers and casting buyers can only obtain the real picture about either process’ performance by developing an open dialogue with their component suppliers. Both parties have the same interest in product design, quality and cost. This dialogue will ensure that the real problems will be identified and real solutions found.

China Increases Export Tax Rebates Amid Risks of Export Slowdown

• Nov 12: China plans to raise export tax rebates(third time since Aug) for some labor-intensive goods and mechanical and electronic products starting Dec 1. Adjustment in export tax rebates will apply to 3,770 goods (27.9% of total exports). It will also eliminate export duties on some steel, chemical and grain products, and reduce export duties on some fertilizer products
• Measure aimed at supporting SMEs as exports and growth are expected to slow ahead, even as increasing rebates might raise trade tensions with the U.S.
• China has reinstated some of the tax rebates it removed in 2005/6 as export sector faces pressure from stronger RMB, higher inflation and slowing demand from export markets. It cut tax rebates on energy-intensive exports and those causing 'trade friction' in 2007. It has also increased new tariffs
• China to end its quotas on textile exports to US and EU imposed after the expiration of the multi-fiber agreement amid slowing growth of textile exports. The annual growth rate in 2008 has dropped to 8.1% yoy, comparing to a 20% in 2007. Textile exports to the US have tumbled to 1.4% yoy to $136.9 billion in the first three quarters from as high as 28% one year ago (Caijing)  
• Tax rebate increase may have limited effect, as it could just contribute to a price war as producers seek to lock in deals in an oversupplied market - it may defer restructuring (Caijing)
• While exporters’ profit margin will be immediately raised as rebates are increased, their total profit is unlikely to improve significantly given the rapidly deteriorating external demand meaning the outlook for exporters should remain gloomy through next year (HS)
• Tax rebate on a range of textiles and garments to rise from 11% to 13% in August. China exported US＄49.96b garments and accessories, a 3.4 5 y/y increase, compared with a 20.9% y/y increase (via Caijing) in 2007
• Girma et al: incentives contributed to export growth
• Seyedin: The end of rebates has raised the cost of manufacturing many goods by 14%- 17% at the factory level (via Business Week)
• Removal of incentives could have been factor in slower export growth in Q4 2007 and Q1 2008

BEIJING -- Intensifying efforts to bolster its economy, China announced a series of business-friendly tax changes aimed at helping companies sell goods overseas.
It was the third time since late summer that China has increased export tax rebates. The government also said it will eliminate export duties on some products after new data provided further evidence the economy is cooling.
The moves, aimed at keeping China's export engine humming amid a global economic downturn, came as fresh retail and money supply data confirmed the country's economic growth is weakening.
Reflecting an easing of domestic consumer demand, China's retail sales growth

• Chinese Growth Slows Sharply: What Is the Risk of a Hard Landing in China?

•  China's GDP growth slowed to 9.9% in the first three quarters of 2008, or about 9% for Q3 alone,  the fifth consecutive quarterly deceleration and lower than expected. Jan-Sept 9.9% growth is the slowest in five years and almost 2% lower than 2007 pace - Further slowing is likely in Q4 and with 2009 perhaps below 8%, a level at which China will be unable to create new jobs, despite recently announced stimulus package
• IMF lowered estimate to 9.7% growth in 2008 and 9.3% in 2009. private sector estimates for 2009 are even lower with consensus now expecting 7-8% (Citigroup - 8%, Morgan Stanley - 7.5%, Credit Suisse 7.2% StanChart - 7.1%)
• The economy will likely continue to decelerate over the next three quarters before bottoming out by mid-2009, and stage a modest recovery in 2H09, as external demand starts to improve and the effect of the pro-growth policy kicks in, and growth recovers to 8.5% in 2010. The policy mix of “proactive fiscal and moderately loose monetary policies” is stronger than the one adopted in the aftermath of Asian financial crisis. (MS)
• In a country with the potential growth of China hard landing would occur if the growth rate of the economy were to slow down to 5-6% as China needs a growth rate of 9-10% to absorb about 24 million new workers joining the labor force every year - macro indicators suggest China is heading for a hard landing (Roubini)
• Unicredit: Fiscal and monetary stimulus  may help to avoid a dramatic slowdown, i.e. an outright recession. But it is definitely not enough to prevent a severe slowdown in economic growth to  7%-8%. China will experience sub-par GDP growth over the next two years at least– weighing on global growth as well as on demand for commodities 
• Industrial production continued to slow in September to 11.4% (12.8% in August and 16.4% in H1) and PMIs suggest manufacturing is in contraction. Urban Fixed Asset investment has slowed in real terms as the cost of investment goods has appreciated.  Domestic demand provided much of the growth momentum, with exports detracting from growth (HS) Slowing housing sector, indicators like commodity demand point to even slower growth ahead
• China likely to take further fiscal and monetary steps to promote growth particularly as slowing inflation provides an opening. It already cut interest rates, reserve requirements and loan curbs and reinstated export rebates and announced a large spending package
• Chinese macro- economy early warning index  stood at 105.3 points in September, 2.7 points lower than August, dropping for four straight months.six of ten components -industrial production, fixed assets investment, import and export volume, profit of industrial enterprises, loans of financial institutions, M2 and urban consumption remained in the "green light zone" in September.But Consumer retail sales and disposable income of urban residents were in the slightly-heated "yellow light zone", while the fiscal revenue was in the slightly-frigid "blue light zone".
• January-September export growth by value slowed to about 20%, down from 28.9% in the year- earlier period and the weakest consumer confidence since 2003 (SARS) may mean that consumer spending (retail sales have grown at about 17% in real terms for the last four months) is overstating the private consumption outlook
• Wachovia: the recent slowdown in Chinese economic activity including industrial production may be exaggerated somewhat by the shutdowns associated with the Olympics, but the trend pace of Chinese economic growth appears to have downshifted
• BNP: Private consumption may be hurt by lower exports,  the lagged impact of the inflation hike of late 2007-early 2008, a softening labor market and falling stock prices
• WB: China’s economic growth has moderated to a more sustainable pace in line with slowing global growth. Declining net exports are partly offset by rising domestic demand
• MS: domestic demand is being supported by government policy to cushion against an external demand slowdown . Should external demand disappoint further, the government may step up spending on investment to support growth
• ADB: Little evidence that China is rebalancing away from investment-led growth, but it is shifting investment sectors. Risk of entrenched inflation and overheating in some sectors

Chinese Industrial Production Slowing, Manufacturing Contracting

• Industrial growth rose only 8.2% y/y in October, the smallest gain in 7 years, the fourth consecutive decline and a steep decline from 17% growth reported in March. Crude steel (-17% y/y), electricity (-4%, the first fall in a decade), steel and auto as exports showed the sharpest declines though output of cement and raw-coal also slowed. Meanwhile surveys of purchasers suggest manufacturing, which accounts for about 40% of China's GDP, is contracting
• Peng: the slowdown in production growth was even more rapid than during the Asian financial crisis a decade ago and illustrates why 5% growth is possible next year
• UOBKH: Slower than expected industrial production growth confirms Olympic production restriction was not the only factor that caused the Q3 slowdown, but rather the weak domestic and external demand and indicates why government officials brought out the fiscal policy response. IP results suggest that without the fiscal stimulus growth might slow to 7%
• Chinese Purchasing Managers Index (PMI) collected by China Federation of Logistics & Purchasing for manufacturing fell to 44.6% in October, the lowest since data collection began in 2005 and the third month of the last four in contraction.  Separately released PMI by CLSA fell further to 45.2 in October, from 47.7 in the previous month
• 9 out of 11 sub indices showed contraction - Output, New Orders, Input Prices, Purchases of Inputs, New Export Orders, Imports, Backlogs of Orders, Stocks of Major Inputs. Output index fell to 44.3 from 54.6 in September, while new orders dropped to 41.7 from 51.3, while the inventory index climbed to 51.4 from 50.5 (Li and Fung)
• Danske: the drop in the PMIs is consistent with the recent slowdown in industrial activity indicating considerable downside risk on both industrial exports and industrial activity. y/y growth in exports could end up in negative territory. Furthermore, the decline in total orders has been even stronger than in export orders. The decline in construction activity  is without doubt a major contributor to the recent weakness in industrial activity in China
• Citi: With the biggest declines in new orders, input prices and output indices, a micro level deterioration may be worse than macro level where government can support output
• WSJ: Some economists tracking the PMI data say the CLSA index better reflects current economic trends, while the CFLP index, tends to be a better indicator of output activity in the coming couple of months.
• Coastal regions are facing some of the most extreme cost pressures as exports slow. Government has reinstated some of the export rebates that were cut in 2007. Government policy encourages lower energy use or relocation of energy intensive production to the poorer regions but these regions often lack the labor, infrastructure and transportation to be real replacements
• Annual migration of workers from interior to the coast has slowed - Guangdong Labour Ministry :11% of the workers did not return after the holiday (via Economist). Guangdong province is trying to transform their labor-intensive manufacturing-based economy into a primarily service sector base
• MS: The economic growth outlook and changes in the external terms of trade represent bigger risks to profit margins than rapid price increases in certain sectors
• FT: labor costs in China remain up to 95% lower than in high-wage nations such as Germany and the US.
• Federation of Hong Kong Industries predicts that 10% of an estimated 60- 70K Hong Kong-run factories in the Pearl River Delta will close this year
• India, Vietnam, Thailand are eroding China's advantage due to cost pressures and an appreciating currency (AmCham) But access to China's domestic market and costs of shifting supply chain are keeping others in China.

India's Industrial Production Slowing: India Inc. Takes a Hit From High Interest Rates and Global Slowdown

• Industrial production continued its slowing trend in Sep, growing 4.8% after the 1.3% growth in Aug (which was smallest in 10 yrs); Manufacturing sector also grew by only 4.8% after the 1.1% growth in Aug (which was weakest since Oct 1998); core industries also slowed; commodity-based industries face slowing demand
• Indian firms facing high lending rates and credit crunch (esp. small firms), raw material and input costs (high fuel and commodity prices);
• declining stock market affecting IPOs, capital raising activity and might affect capex, esp. in infrastructure sector and small and medium enterprises; Global liquidity crunch will affect overseas capital raising, cross-border M&A thus affecting the recent investment boom
• forecasts for corporate earnings, dividends revised down-->Net corporate profits in Apr-Jun-08 hit a 11-quarter low
• Kotak: Cyclical trough in industrial growth might last through mid-2008; export slowdown will have less impact on industry; easing input prices ad interest rates support growth in 2009
• EIU: High inflation, interest rates, slowing consumption is slowing industrial production, deterring firms from investing in capacity expansion
• Amid high inflation, govt is forcing private sector to absorb high production costs and squeeze profit margins rather than passing on higher prices to consumer; govt contemplating price controls for several commodities and metals which may hit producers; price/export restrictions on some products (steel, cement) also preventing producers to benefit from high global commodity prices even as slowing global growth may hit export demand
• M&A activity in H1-08 declined (first time since 2004); volume of M&A and PE deals down 15% y/y; no. of deals was down 8% y/t ; avg deal size down 7.7% y/y/ ; more number of deals in Q1 but larger deals in Q2; Strategic investments continued to dominate M&A activity with 70% share; share of foreign investors in deal value down from 78% in H1-07 to 67% in H1-08
• Energy (losses of oil companies), real estate (slowing capital inflows, price correction), IT (slowdown in U.S.), banking (interest rate hike, losses on credit derivatives, rising NPLs), auto, consumer durable (slowing consumption, income growth and fuel price hike) may take a hit; infrastructure projects also hurt by higher raw material and borrowing costs and declining net returns
• Corporate deregulation, easing overseas investment norms behind recent growth of India's pvt sector; rising capacity, economies of scale, movement to high-end, high- technology, value-added production and exports, domestic and cross-border M&A in recent years; challenges: Shortage of skilled labor, wage inflation, less developed corporate bond market, govt restriction on foreign investment in several sectors

India Inc. Takes a Hit From High Interest Rates and Global Slowdown