New Opportunities with Open Die Forging

In their never-ending search for ways to increase production efficiency and develop new capabilities, gear manufacturers should take a look at this time-proven process.

0
658

True, the unsteady recovery and realigning markets mean business is more difficult for the entire gear industry. Order volumes are lower, sales in historically profitable markets are down, and competition is stiffer. But it’s also true that opportunity is out there, it just might not be in the same places it was before. Today’s gear manufacturers must be flexible enough to go after new business while continuing to protect their existing business. Fortunately, an extremely versatile and highly efficient manufacturing process already exists to benefit the gear industry. Open die forging is flexible, creative, and cost-effective, giving you the competitive advantage you need to find new business and keep your current customers coming back.  
 
Old Process, Fresh Take
The open die method of metalworking takes on significant new relevance in today’s complex global marketplace. Open die forging is distinguished by the fact that the workpiece is never completely confined or restrained by dies during the forging process. Most open die forgings are produced on flat dies and are often associated with larger, simpler-shaped parts such as bars, blanks, rings, hollows, or spindles. But with the use of in-house or customized tooling, custom forgings approaching closed die configurations can also be achieved. This “hybrid” open die forging process offers gear manufacturers shape, size, and material flexibility, lower volume requirements, and potential savings across the entire manufacturing spectrum. All this in addition to the higher quality and increased strength you’d expect from forgings. Compared to other metalworking alternatives such as round bar machined to multiple diameters, fabrications or weldments, castings or torch cut plate, open die forging gives manufacturers the competitive advantage they need to succeed in new markets. Even against impression or closed die forgings, open die parts can be more cost-effective or timely. See fig. 1, fig. 2, fig. 3, fig. 4, fig. 5, fig. 6 for examples of the tooled hub forging process.

No Limits, Less Cost
When it comes to shape versatility, the only restriction is the imagination of the customer’s engineers and the forging supplier. Tooling and craftsmanship play a hugely important role in this process. Loose tools—simple ring or pot die forged tools, for example—are used during the forging process to impart more shape to the work piece, such as hub projections, or webbing. The utilization of these tools brings closer to near net shape innovation with high levels of creativity and consistency to the end product. Instead of welding together two parts, for example, gear manufacturers have the option to purchase a single integral forged part, which saves time and money and creates a stronger, higher-quality finished piece.

However, shape versatility isn’t the only reason for choosing open die forging. Size and quantity limitations are nonexistent, as well. A gear produced by open die or rolled ring forging can weigh anywhere from a few pounds to thousands of pounds. And since virtually all open die and rolled ring forgings are custom-made one at a time, this process remains a cost-effective way to quickly produce one-at-a-time prototypes as well as low volumes. The lower volume requirements give gear manufacturers who may currently utilize impression or closed die forgings the option to order only what they need, when they need it, instead of being subject to order minimums. This can save money upfront as well as allow for lower inventory levels, protecting manufacturers from the highly volatile material costs so evident in today’s economy. With no restrictions on size and order quantity, gear manufacturers are competitively positioned to continue servicing existing small volume customers and explore additional business opportunities at a lower cost. See fig. 7 for a comparative analysis chart.
 
Near Net Shapes, Far Out Savings
Material savings are another benefit of this process. A stepdown spindle provides the perfect example. Some other metalworking processes require removing excess metal from existing shapes, such as machining a stepdown shaft from a solid bar or forming a hub from a torch cut plate. The removed material simply goes to waste—material that was purchased, transported, and turned to scrap. But the same part manufactured by the open die method yields the stepdown shaft or hub shape during the actual forging process, therefore requiring far less subsequent removal of material. There is less waste in the end, customers realize more savings, and gear manufacturers can confidently pursue opportunities with a more-efficient, effective solution. A material savings example is shown in fig. 8.

Since the initial forged shape is closer to the net shape than round bar is, it requires less machining, which saves process time and extends tool life. So in addition to the tangible materials cost savings, the availability of high quality, cost-effective forgings with short lead times create supplementary value.

A Multitude of Materials
Open die forging supports a variety of materials important to the gear industry in both ferrous and non-ferrous metals: carbon, alloy, stainless, tool steel, aluminum, titanium, and nickel- and copper-based alloys. From through-hardening, carburizing, “H” Band, AMS, and MIL-S-5000 to AGMA, bearing-quality, wind turbine, nuclear, and other power generation grades, open die forging meets the demanding specifications of your customers every time.  

Unparalleled Strength
Yes, open die forging brings extraordinary flexibility and cost-effectiveness to gear production. It also provides superior directional, structural, and impact strength and integrity. By mechanically deforming the heated metal under tightly controlled conditions, open die forging produces a deliberately oriented, contoured grain flow that improves mechanical properties and metallurgical soundness. Referred to as directional strength, this result is obviously beneficial to bottom line gear quality and is unique to the forging process.

Proper orientation of the grain flow, along with proper grade selection and thermal processing, can meet virtually any impact requirement for gears. In addition to producing contoured grain flow, open die forging also reduces the grain’s size. The added strength ultimately means longer product life, and it’s only available through forging. When stepdown shafts are being machined down from a round bar, their unidirectional grain flow is cut, exposing the grain ends. Impact strength is compromised, rendering gears more susceptible to fatigue and more sensitive to stress corrosion cracking. See fig. 9, fig. 10, fig. 11 for examples.

The net sum of the open die (and also rolled ring) forging process in terms of strength is that it greatly improves gear quality. As players in the gear industry strive to stay competitive and grow market share, opting for open die forged gear parts offers a level of quality that will win the customer’s confidence and create long-term business relationships throughout the entire supply chain.

The Right Partner
Once a gear manufacturer decides to pursue forged parts, it is important to find a forging partner that brings all of the benefits of process to the table. Forming a relationship with a “one-stop shop” forging partner that has a wide array of open die and rolled ring gear part capabilities will give you the flexibility you need to explore additional business opportunities. Additionally, suppliers with years of experience, a willingness to share references, and the production expertise of similar parts are more likely to deliver the value you need, when you need it.

Make sure the supplier has the most advanced equipment necessary and an extensive tooling inventory level to deliver the desired gear parts, no matter how complex. Also ask about the in-house capabilities of secondary services such as machining, torch cutting, heat treating, and testing. You should see trained, on-site metallurgists able to provide insight and assistance with the selection of optimum alloys. The supplier should also have a sufficient inventory of gear industry-specific material grades, coupled with the knowledge of custom-melt and specialty alloys. Any service that goes outside the primary supplier adds time and cost, and in some cases compromises quality, so choose a one-stop shop partner.

Insist on quality control, as well. Suppliers should be ISO 9001:2000, DNV Certified, SNT-TC-1A compliant. Chemistry verification on both incoming raw materials and outgoing forged products should be standard procedure. Any supplier that does not give quality control its proper due is probably not the best choice as a potential partner.
Finally, a supplier’s practices should demonstrate an overt commitment to customer service. Look for programs such as guaranteed delivery, breakdown service, quick quote turnaround, and fast response rates. The goal is to find a supplier interested in forming a synergistic, cooperative business relationship from which both parties benefit over the long-term.

Getting into Gear
Open die forging, especially in the gear industry, is nothing new. But it is clear from the numerous benefits it provides that its appeal is more relevant now than ever. Take another look at open die forging. There is no time like the present to embrace the advantages open die forging gives you today, and the potential it promises for tomorrow.