Machine shops face competition from not only regional competitors, but also Pacific Rim manufacturers that are vying for work.
Maumee, Ohio-based Hammill Manufacturing’s Impact Cutoff Division uses precision forging, also known as net-shape forging or closed-die forging, to compete with foreign companies for lucrative contracts. The company has converted 36 gross forgings into 36 precision-forged part numbers for a global hydraulics manufacturer.
Impact Cutoff says adapting the traditionally high-volume warm-forging process to small (25,000 parts or less per year) and medium (about 300,000 parts per year) lot sizes has been the key to its success. According to John Hammill, president of Hammill Manufacturing, the precision-forging process is ideal for low- to mid-volume part runs that involve high machining content, significant material loss and parts that are not currently being forged.
“Typical parts that can benefit from precision forging include bulk manifolds, side and pinion gears, connecting rods, hydraulic components and other high-machining-content parts,” Mr. Hammill says.
Impact Cutoff maintains tolerances of ±0.0025 inch on its precision-forged parts. The company has produced more than 45,000,000 total parts over a 17-year period with only three rejections—a 99.99 percent quality performance. Overall, the company has a 17-year history of 100 percent on-time delivery for the precision-forging process.
The precision warm-forging process has reduced the company's total part costs by as much as 25 percent. The process reduces material scrap, eliminates or reduces subsequent finishing operations and lengthens perishable tool life. In addition, the process produces a forging blank that is stronger than other conventional forming methods, and the resulting formed parts have lower total part costs than those produced with gross-forging processes, the company says. In addition, the company says, the precision warm-forming process is a viable alternative to screw machining.
One major benefit of the precision forming process results from induction-heating the forging blank prior to forming. According to the company, induction heating ensures that each formed part has a consistent, uniform hardness without hard spots or other material deviations. Uniform material hardness can result in predictable and consistent material characteristics, which in turn can improve machinability and increase cutting tool life. In addition, the process creates consistent, unidirectional grain structure in the forged part. As a result, the precision-formed part is stronger than conventional forgings, castings or parts machined from barstock, the company says.
Precision forging has reduced the company’s metal scrap by as much as 30 percent. The precision-forming process uses a “closed-die” approach in which the entire forging blank is encapsulated in the die cavity. The forging blank length and weight are tightly controlled, resulting in no material waste. The entire forging blank is used in the formation of the part—no material is scrapped because nothing protrudes from the die, and no part trimming is required. Because of the closed-die nature of the process, the parts have no flash lines, material scaling or parting lines.
Impact Cutoff has a turnkey manufacturing process with in-house capabilities for tooling design and build, prototyping, manufacturing and prove-out. The company uses “Double D” 12L14 and 1215 cold-drawn steel, but the process could also work with materials such as stainless steel, brass and titanium.
Initially, steel barstock is cut off to precise gram weight and length tolerances. The company controls weight closely to ensure a near net-shape forging without flash lines. The steel blanks’ ODs range in size from 0.25 inch (6 mm) to 2 inches (50 mm). Height ranges from 0.25 inch (6 mm) to 3 inches (75 mm), and weight ranges from 0.10 pounds (45 grams) to 3 pounds (1,400 grams).
The steel blanks are then tumbled and water-washed in preparation for forging. These preliminary operations remove burrs and lubricants that can cause carbon buildup within the die. The blanks are then stored in bulk bins.
An Allen Bradley PLC provides process control to ensure proper temperature, part positioning, press operation and robot arm movements for automated part loading and unloading. The control system’s logic provides increased reliability by preventing crashes and part jams.
Material handling plays an important role in the manufacturing process. Blanks drop onto an automated loading table and individually feed into the heater induction chamber via a Dyna-Slide vibrating platform. Manufactured by Lipe Automation Equipment of Rochester, New York, the Dyna-Slide orients the parts for automated loading within the die. The vibrating system allows the part to travel on precise paths without touching the sides of the loading feeder. The controller senses when a new blank needs to be fed into the queue.
The steel blanks are then transferred onto a feeder through an electric-powered induction heater. The water-cooled electric heater provides temperatures ranging between 1,100 and 1,400°F. The blanks are heated to the targeted temperature and gravity-fed into a staging position perpendicular to the die.
The heated steel blank is then “grabbed” and presented to the die in a horizontal position by a GEVA cam-operated, pneumatic robot arm. Video cameras verify temperature, part position and part orientation before the press closes. The GEVA then returns to the original staging position.
A 400-ton Verson vertical press reshapes the pliable steel blank to the exact dimensions of the die. The closed-die process leaves no metal scrap, flashing or waste by-products because all the metal stays contained within the die cavity. At the end of the press cycle, an air blast and ejection pins eject the part, which is then dropped onto a slow-moving conveyor for air cooling. The formed part is quenched in a two-stage water bath and transferred into a completed-parts bin before being prepared for shipping direct to the customer.
“Precision forging has helped Impact Cutoff level the playing field with low-cost, low-wage foreign producers by lowering production costs,” Mr. Hammill says.