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CNC tool grinding can improve the output quality of any screw machine operation. But there are a number of factors to consider when deciding whether to send tools out or grind them in-house: the volume and variety of tools; complexity of the tool versus programming and operator skills available; tool inventory required for production; and capital and labor costs. The key is to be able to decide how to assure the best tool for the most economical production.
For cutter grinding, software is increasingly providing the machining skills that once were the domain of experienced operators. This is as true at screw machine shops as it is anywhere complex 3D geometry, difficult materials, extreme tolerances and short lead times are typical. CNC can be helpful, but an operator must understand the tool that is programmed and therefore how to adjust the program to accomplish fine improvements in the tool geometry.
For many screw machine shops, manual grinding is not good enough or fast enough. Training time for operators on CNC tool grinders, however, is often Windows-based and menu-driven, reducing the time tremendously. For example, learning proper grinding and end mill sharpening on a manual machine could take 6 months. To operate a CNC tool and cutter grinder, reading a micrometer is about all that is required.
Most in-house tool grinding operations are not a primary candidate for a company's capital investment dollars, so most in-house departments do not have the latest, most efficient equipment or software—unless they are sharpening large volumes of tools, such as occurs at Metal Seal & Products, Inc., a Willoughby, Ohio, screw machine company that produces more than 80 percent of the tools it uses in-house. The company makes mainly brake pistons and cuts aluminum, brass and a wide range of steel grades.
The company had a couple of manual three-axis tool grinding machines and an older CNC grinder that were producing accurate tool geometries. However, the final product could vary according to the operator producing the tools. At the same time, the CNC machine was cumbersome to program and severely underpowered, according to Steve Blaha, manufacturing engineer at Metal Seal.
Being able to turn around the tools in hours rather than weeks is particularly valuable to our operation, and we needed the flexibility to produce small lot quantities of tools from solid stock," Mr. Blaha says. "That's why, 3 years ago, we purchased an ANCA TGX CNC tool and cutter grinder. Grinding in-house has provided us the capability to grind almost any geometry we need in less time and at less cost than sending it out would require. Additionally, if a tool has to be modified or repaired, we can do that in-house very quickly. The result for our customers is reduced lead times for delivery of their parts." Tools are ground from solid carbide or HSS with flutes, trepans and any number of complex features.
With the ANCA ToolRoom software Metal Seal uses, only a minimum of parameters are needed to program the machine for each tool. This is key to fast setup. Engineers design the tools, and the operator programs the tool at the ANCA tool grinder. Once programmed, a smart probing system in the machine tool identifies each tool, automatically determining most tool geometry required for grinding. Programs are stored in the machine control for ready access, saving time.
Tool grinder capabilities and software suites have substantially replaced the skills tool grinders learned over many years in the tool crib. But even if a tool was generated perfectly according to the CNC program, there is still no substitute for the operator's ability to recognize a tool that will actually accomplish the assigned material removal task, according to sources in the industry. At Metal Seal, the ANCA operator is an experienced manual grinder hand who understands tool grinding and geometries.
Metal Seal still sends some tools to be produced outside, as those vendors have been producing the tools for years and provide good service. It keeps in-house the high volume tools and tool development.
The first question a firm should ask when considering tool grinding in-house is a volume question. At Metal Seal, a large volume of tools to grind and regrind helped to justify bringing tool grinding in-house. To resharpen a $50 tool, for example, would not be worth the cost of a $250,000 and up (to $500,000) piece of equipment plus software, personnel and training.
In-house tool grinding is most economically and efficiently accomplished with a family of tooling, such as with a screw machine shop consuming hundreds of tools a week. At Metal Seal, the tool grinder produces more than 1,000 unique tools as part of a tool management system that services more than 100 screw machines, filling tooling orders that are typically six pieces or fewer. Tooling inventory is thus kept to a minimum.
Further, in-house capability is also used for prototype work and tool development and rapid program modification. Feedback from the floor is possible right away on tool geometry, and a correct tool can be returned quickly—a big impact on part quality and production.
But for some companies, tools requiring a lot of operator involvement and setups/teardowns should generally be left to an outside source that has the skills and software necessary to produce a wide range of tools.
A company that has a toolroom and the skill sets to operate it and that likes the quality it is getting should spend the money to upgrade to CNC. For screw machine shops, there is also an advantage to designing and producing their own tools in-house from blanks. In-house quality can save the expense of an incorrect tool.
In some instances, as at Metal Seal, an experienced operator is able to improve a tool's machining characteristics (speeds, feeds and depths of cut) with proper setup and a CNC's grinding consistency, compared to grinding with a manual machine tool at a machine that is set up by an operator who does not see the tool often.
Some companies upgrade their equipment because tool geometry has changed so much over the years that an older machine and software no longer have the capability to handle the new more complex tooling. The machines don't wear out; they simply fall behind in technology and capability. This is what Metal Seal found when it purchased its first ANCA grinder.
Whether tool grinding occurs in-house or at a grinding service, the productivity of your machining process will be assured with a tool that is the same cycle after cycle. There are cost and quality advantages to both outside grinding services and in-house tool crib operations. The most cost-effective decision for your firm will depend on the variety, complexity and volume of tools you use in your machining.