A Perfect Pair: New-generation CNCs and Custom Tooling

A spline cutter was developed to replace standard tools that cut one groove at a time around a cylinder perimeter. With the special tool, production time was 10 times faster and tool life was increased.

The advent and proliferation of CNC machine tools caused the manufacturing industry to question the value of custom tooling. At one point it was thought that special tools would no longer be required. The reality, however, is that custom tools are more important than ever to obtain the quality, accuracies, and efficiencies required by an industry that has embraced automation.

Many companies invest in the latest generation of machine tools but fail to put as much value into what goes on the end of the spindles, and how best to approach production of individual jobs. Quality tooling is a critical part of optimizing performance of any machine tool, and some jobs warrant investing time and funds in special tooling. It’s a matter of getting more bang for the buck.

A custom tool can meet a single objective for a customer, or a combination of several. A special design can:

• Create a unique shape or detail not possible with offthe- shelf cutting tools.
• Satisfy a relationship or tolerance requirement of part features not readily obtainable with multiple tools or in separate operations.
• Optimize surface finishes, cycle times, or tool life.
• Reduce the number of tools and tool changes to minimize cycle time or fit the number of positions in the machine’s tool magazine.
• Extend tool life and regrindability

A typical custom tool user is a company looking for a second tool to finish a hole detail. A custom tool could combine the two steps into one and complete the feature in a single operation. Along with a reduced number of tools, the company reduces production time and potential for error. In many cases, secondary workholding is also eliminated.

Complex features like chamfering of a detail on the underside of a part can be simplified. If the part is held in a particular way, a tool may be produced that can get in and around the part to machine the detail without flipping the part.

Different Levels of Custom

Although most shops can identify the need for a special tool, many need assistance to define what is really required. Most custom tool users fall into one of four categories.

1. There are those who don’t know exactly what they are looking for but know that they need something beyond standard tooling. This user, typically the most open to suggestions, will usually provide a part drawing or sample and be very forthcoming with application information.
2. Some shops start with an idea of what will meet their needs but are open to suggestions and innovation. They usually provide a part drawing or sample, possible machine approaches, and a basic tool design.
3. Others simply want a fabricator. They have defined what they need and approach the custom tool manufacturer with overall tool dimensions. Perhaps they need some assistance determining cutting geometry.
4. Then there are those whose production will often dramatically benefit from the introduction of a special tool. Entrenched processes using standard tooling may be in place and consideration has never been given to purchasing custom tooling.

Unexpected Production Improvement

One shop, for example, was machining 1,500 serrations along the length of a cylinder one groove at a time. Production of each cylinder wore out multiple standard tools, which added process time to reposition each new tool to the part. The company looked into custom tooling in search of a way to improve tool life.

After analyzing the job, it was determined that a special tool could do much more than just reduce tool changes. A spline cutter that simultaneously cut 10 serrations in the arc of the cylinder radius was developed.

Net benefits included the original objective of extended tool life with a custom tool that lasted for multiple parts and could be sharpened inexpensively; parts that could be machined 10 times faster; and greatly reduced deburring time. Better contact with the workpiece also reduced vibrations during machining, improving quality.

The cost of the special tool was recovered after machining the first part. The tool reduced the production cost dramatically and improved part quality without significant upgrades to the machine tool. This success led to additional custom tools developed for each of the parts in the same family of cylinders and a revamp of the machining process.

A spiral profile cutter is shown next to the part it produces.

Multiple Design Aspects

Despite the fact that there are different expectations about what a custom tool will accomplish, each design process requires similar information and is approached in much the same manner.

Many factors are considered in the development of a special cutting tool, starting with a part drawing or sample part and the tolerances that need to be obtained. The material being machined, the machine to be used, and the number and order of operations are verified. Coolant, whether through the tool or a flood around the tool, is a part of the design.

A custom tool expert will look at the part from a cutting tool perspective to identify operational details that will create efficiencies and process adjustments that may not be apparent to the shop, such as combining chamfers or radii with adjacent surfaces or, conversely, creating sharp intersections that do not need deburring. Effective tool design often can eliminate deburring of critical surfaces or control where burrs are generated, leaving them in an area that is less difficult to deburr.

Tool life is also part of the design process. The correct substrate, cutting geometries, integrated coolant feed, and coatings are chosen to extend the life of the tool and allow multiple regrinds that bring the tool back to original cutting capabilities.

A key element in the timing of developing a special tool is the blank. If the tool can be made with an off-the-shelf blank, it can most likely be designed, produced, and making chips in less than two weeks. A highly complex tool, however, can take up to eight weeks or more to engineer and manufacture.

High-performance tools can appear to be fairly expensive when the initial cost is compared to standard tooling, but an analysis of reduced production time, improved quality, increased tool life, and less part cleanup can result in a very quick ROI—and a competitive advantage.

www.castelartool.com

Renato Evola, president of Castelar Tool & Grinding, produces special tools on one of the company’s multiaxis CNC grinding machines.