Ensuring Zero-Defect Bores

Today’s cars are a lot safer than the cars our parents drove. That’s partly because of passenger safety features such as air bags, ABS and seat belts—and the fact that those safety products are made to exacting standards to ensure that they’ll work when and if they are needed. Companies that produce the components that go into those safety products must produce them defect-free. One bad part in a million is one bad part too many. Fortunately, those companies are getting a lot of help from equipment manufacturers that are coming up with the machines and systems needed to achieve defect-free parts.

For example, American Turned Products (Erie, Pennsylvania) has been a supplier of parts to the auto industry since the company started in 1984. Automotive parts currently account for about 70 percent of the company’s sales. It has always had bore sizing and finishing capabilities. According to Harry Eighmy, vice president of manufacturing, any company supplying parts to the auto industry must have that capability, especially now more than ever.

“今天的工作更苛刻，而不是20年前，”Eighmy先生解释道。“随着技术的改善，客户想要并期望更严格的公差和更好的饰面。公差是10年前他们是三分之一的一半。“

Until a few years ago, the company had been using conventional-stroke honing equipment exclusively. However, during a visit to International Metalworking Technology Show, employees saw a demonstration of a single-pass bore-finishing system that uses multiple diamond-coated tools. The multiple-tool system, made byEngis Corporation（伊利诺伊州的轮班），显着优化了美国转型产品（ATP）的设备。该公司购买了该机，并在第一次在展会中看到它的90天内运行并运行。

The honing equipment that ATP had been using has a rotating hone that reciprocates in and out of the bore, expanding slightly in diameter with each stroke. The “stone,” or honing tool, is made of a fine-grained abrasive that wears slowly, permitting fine control of the bore size and finish.

By contrast, the system consists of multiple, solid, cylindrical tools, each slightly larger in diameter and arranged in increasing order of size. Instead of conditioning the (blind or through) hole by means of multiple passes with a single, expandable-diameter tool, the single-pass system conditions the hole using a single pass of each of the progressively larger diameter diamond-coated tools.

虽然钻石工具听起来很贵，但据说比传统的珩磨工具便宜。金刚石工具不仅具有高度耐磨性，而且磨损分布在几个工具上（根据应用，多达八个）。因此，孔隙表面与部分更加一致，并且机器在刀具变化之间运行较长，导致更大的吞吐量。

Typically, the part with the bore to be finished is loaded in a fixture on the machine’s turntable. The turntable rotates the part to the first station where the first (smallest diameter) tool makes a single pass. The turntable then indexes the part to the second station where the second, larger diameter tool takes another pass. The turntable continues to index the part until all of the progressively larger diamond-plated tools have taken a pass at the part. Every time the turntable indexes, a bore is processed at each workstation and a finished part is completed.

As is the case with most metalworking processes, the machine is only one factor in the bore-finishing equation. Other factors, such as tooling, fixturing, coolant and part loading/unloading, must also be taken into account to ensure a successful application. Accordingly, Engis representatives are available to customers to help with installation. They visit the customer, examine the intended application and recommend the most productive tooling arrangement, part fixturing arrangement, coolant, part inspection, automation options and more. They also do turnkey installations (commonly done for high-volume jobs) to make them as efficient and as mistake-proof as possible.

Therefore, when ATP received a large order for a 1215-alloy, case-hardened steel, automotive part, it relied on the manufacturer to supply an automated system on a turnkey basis to finish a 1 3/8-inch-deep blind bore in the 1-inch-diameter by 2-inch-long part. The bore had to be accurate within ±0.00045 inch, with a 30-microinch finish.

Most of the parts that the company produces are made from steel and are sent out for heat treating before finishing operations on critical bores. For that reason, its bore-finishing equipment is grouped in one area instead of being combined with production machines, such as multi-spindle cam automatics in dedicated production cells. Currently, the company has two manually operated Engis bore-finishing machines and the automated system developed for the automotive part.

机器人装载/卸载

In the automated system, discrete, heat-treated parts are fed to a bowl feeder that positions them in a delivery chute. A compact Fanuc robot, located in what would be the operator’s position in front of the machine but inside an overall enclosure, takes a part from the delivery chute and delivers it to the loading station on the machine’s turntable. For this cylindrical part, the part fixture is a simple collet.

The turntable indexes to present the engine timing part to each of the several tool stations. In this case, the part is presented in turn to six progressively larger, single-pass, diamond-coated, bore-finishing tools. When the part indexes around to the exit station, the robot removes it from the collet and delivers it to a chute leading to a bore gaging station. If the part is within specifications, it passes through the inspection station to the discharge chute and to a basket outside the machine enclosure.

Where the customer requires a ±0.00045 inch tolerance on bore size and a 30-microinch finish, the automated bore-finishing system maintains a much tighter (±0.0001 to 0.0002 inch) tolerance spread and a 10- to 15-microinch finish.

When we visited ATP, the same job was running on the automated single-pass bore-finishing machine and also one of its manually loaded machines. Mr. Eighmy pointed out some of the advantages of the automated machine. “The automation package is not very expensive and only takes up about half again as much space as the manual machine,” he notes. “Cycle time (9 seconds) is the same for both machines. However, the automated machine runs continuously. Our studies have shown that we’re getting a 30 to 40 percent improvement in output with the automated machine.

“可能是最重要的考虑the automation removes the possibility of human error,” Mr. Eighmy continues. “It ensures that every part will be processed in exactly the same way. That’s the only way we can be sure of achieving zero-defect parts.”

Additional Automated Machines

自动钻孔加工机器对公司的重要性可能是其对更多机器的计划。该公司拥有两台手动机器，用于小型工作，并提供适度的零件数量，同时升级程序。它计划用自动化包装改装手动机器，并将购买另一台自动化机器，该机器将与现有机器一起安装。运行该部门的钻孔精加工机器的两名运营商也将负责运行第四台机器。这意味着公司将以大约50％的钻孔完成能力提高到劳动力成本没有增加。