The Ins & Outs of high-performance machining

Aug. 22, 2001
There's a big difference between high-speed and high-performance machining.

Dan Horn
Senior Applications Engineer
DP Technology
Camarillo, Calif.

High-performance machining involves more than feeds and speeds. It takes a comprehensive look at software, controls, tooling, and machine capabilities to optimize the overall process.

One hallmark of good CAM systems is a strong database of standard machining cycles that are easy to customize as the application demands. Here, Esprit software simulates a finished mold (top) and a plunge-milling operation.


One hallmark of good CAM systems is a strong database of standard machining cycles that are easy to customize as the application demands. Here, Esprit software simulates a finished mold (top) and a plunge-milling operation.

Most manufacturers have three basic goals: To make parts faster, better, and cheaper. Often, meeting these goals requires a change in process, tooling, machine tools, and CAM software. The most expensive of these upgrades is usually the purchase of a new machine tool. However, few companies learn to use new equipment to its fullest potential, neglecting to address all the issues involved in quality machining. Shop floor results are usually disappointing compared to the machine's performance in the showroom, unless users know the basics of high-performance machining.

High speed versus high performance
The term high-speed machining has been a popular expression since the early 1990s, particularly in regard to parts produced by machining centers. HSM tends to be limited to the milling of highly sculpted parts typical to the mold/die and aerospace industries, and usually does not address other common operations such as drilling and boring.

High-performance machining is a more apt term because it encompasses all types of machining operations and involves more than high feeds and speeds. Highperformance machining puts the best, most cost-effective technologies to use on the shop floor. HPM is a comprehensive package that takes into consideration the entire machine. This includes mechanical characteristics, control and servodrive performance, tooling, toolholders, fixtures, part processing, and even machining strategies.

To get the best results, engineers must take into account all aspects of HPM. For example, if the weak link in the production process is tooling, it does little good to purchase a new machine tool without addressing tooling issues as well. Often, manufacturers must deal with several issues simultaneously, because neglecting one or more items means the shop will not realize the full benefit of high-performance machining.

HPM guidelines
Moving toward high-performance machining is a process that takes time. How much time depends on how much effort a shop owner puts into enacting HPM, but it can be a reality for all machinetool users. Here are some recommended steps for a successful transition.

Improvement is priority one. The first step is to make improvement a priority. The move towards high-performance machining must be someone's official job. Not assigning a specific leader for this task will drastically reduce a company's ability to move forward.

Team effort. Improvement must be a team effort. The team should consist of management, manufacturing engineering, and shop-floor personnel. This group must have the authority — or at the very least make strong recommendations — to purchase what is needed to make the desired improvements.

If it is not a team effort, a company will most likely not reach its improvement goals. Far too often individuals would like to improve a process, but have been stopped because they lacked management support. Those who are comfortable with the status quo will need some convincing, but working as a team can build the excitement and momentum needed to reach the goals.

Do the legwork. Once the team has been established, the next step is to see if the shop can get more out of existing equipment. If your company has already decided to buy a new machine tool, the team should concentrate on learning how to best use the new equipment before it arrives.

Start with parts currently in production. Identify the most time-consuming manufacturing processes to establish a point of reference of where to concentrate initial HPM efforts.

Next, contact the machine-tool supplier for advice their applications people can offer about these particular processes. At the same time, develop a relationship with tooling suppliers. Both groups should be able to recommend how to best apply the machine and cutting tools to improve part processing. Often, tooling vendors can supply different tools to test on your parts. Other good sources of information are machine-tool shows, machining seminars, and trade magazines.

Put knowledge to work. Because most mold and die applications are one-of-a-kind parts, these shops can gradually phase in new tooling and processing over several parts. Even on one-of-a-kind parts there are features that require repeating similar machining strategies. After reaching the goal on one process, move on to the next.

If performing tests on actual parts poses undue risk, set up tests in scrap material. The test cuts can be simple straight-line cuts or drilled holes. From my experience as a senior applications engineer for a machine-tool builder, the results of such tests apply to many real-life parts. One example comes from a customer who had just purchased an established mold shop. They regularly machined stainlesssteel glass molds. The vice president of the new company knew the shop was not getting the full benefits from their machinery, and paid a visit to our company to finalize the purchase of a new VMC.

During the visit, we experimented with a variety of cuts similar to ones required on the glass molds, in scrap pieces of stainless steel with some stock tooling. The customer later ran additional tests on actual parts based on our work.

First, he drastically increased the speeds and feeds. Then, he increased the toolpath tolerance and decreased the stepover to reduce hand work. (This made for a longer part program.) The cutting tool and toolholder were already high quality, so did not need replacing. The machining time for one part had been 50 min. After the tests, machining time was reduced to 10 min and quality improved. Same machine, same tool, five times the production rate.

Cheaper isn't always better. The customer mentioned above made a 500% improvement in cycle time with no real investment, just some time to reprogram the part and run a few tests. That may not always be the case. In fact, there comes a time when further improvements are not possible without purchasing a new machine tool. But before going that route, make sure to get the absolute most from existing machines and tooling.

When looking at tooling, machine tools, and software, do not select the lowest bidder without weighing the benefits of higher-priced options. Quite often, a moreexpensive version will lower costs in the long run. Performance is what makes profits, not a low base price.

Invest in a flexible CAM system. Applications engineers are required to program a wide variety of complex parts, often with the assistance of a CAM system. Based on my work with CAM software, in most cases, the best CAM system is not necessarily the one with the most features, but the one with a strong set of standard machining cycles that the user can easily augment. The ideal software enables programmers to create customized routines that extend beyond ordinary toolpaths. CAM that includes Visual Basic facilitates easy customization by supplying an industry standard macro language. Further, users should be able to store their machining knowledge and preferences inside the CAM system in the form of a database that can be accessed for use on any part. In addition, a full library of editable postprocessors should be available so that users can adjust them to suit their specific machining needs.

Realistic simulation that shows the machining in the same manner as the machine would move is also a part of a successful CAM system. This feature is particularly useful on multisided parts machined with rotary tables. When running a difficult part, it helps to have a PC on the shop floor. This lets the user update the toolpath on the PC, simulate the changes in the CAM system, DNC the code to the machine, and start cutting.

Know your partners. Investing in machinery, tooling, and software means not just purchasing a product but investing in a company. Buyers and sellers really become partners, so it is vital to choose your partners carefully. Shops purchasing new equipment, tooling, and CAM applications should look for companies that not only listen to their ideas, but actually incorporate them into practical additions to the product. A good partner company will stick with you and ensure that the return on your investment is truly highperformance machining.

Here's a real-life illustration of the need to examine every aspect of the machine and process to ensure the successful implementation of high-performance machining. A mold shop purchased a new 10,000-rpm, 35-hp vertical-machining center for about $225,000. Shortly after installation, the customer claimed the machine would not bore good quality holes in mold bases.

We visited the customer and observed 1.5-in.-diameter bored holes with a surface finish of 250 rms at best. Worse, measured diameters varied considerably from hole to hole. Investigating the tooling, we determined that the boring tool was an ancient brazed-carbide boring bar, and the drills were high-speed steel twist drills. By substituting state-of-the-art insert drills and boring tools suited for HPM, the resulting drilled and bored test holes were mirror finish round within 0.0001 in.

The same customer also asserted that the machine would not mill. Again, they were using older HSS end mills. By switching to aggressive, indexable insert milling cutters, the cuts removed more material faster than the HSS tooling and the machine handled these cuts with ease. The owner was amazed to say the least. We got out catalogs and ordered upgraded tooling immediately.

In this example, both the milling and boring issues started out as a perceived problem in the machine. As is often the case, the customer had mistakenly thought that the machine had a bad spindle or some other rigidity issue. In reality, with some changes in strategies and tooling, the machine ran the parts faster, tooling costs were lower per part, and the process was easier on the machine.

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