A New Trend in Broaching Technology

An increase from around 2,500 to 7,500 parts between tool sharpenings is just one of the improvements provided by an innovative new design for broaching machines.

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With regards to broaching, is making new technology investments profitable? We see customers making choices based on capital investment costs verses long-term cost per part and quality capabilities every day. As we all consider program capital constraints and build return on investment models, there are necessary choices to be made. In broaching, one company is working to make that choice easier.

Stenhoj Hydraulik Company–headquartered in Denmark with sales and service worldwide, including an office in Michigan–has developed an innovative broaching machine that fits the lean manufacturing model like a glove. This new breed is built employing best practice, from engineering and design to manufacturing and service, all meant to provide users with a tool to secure a competitive advantage. If your company does broaching or is considering a value-added operation to parts you are currently making, the following article should be of particular interest to you.

Several different models of this broaching machine are available, but what makes the Stenhoj design truly different? You only need to see it and hear it run to quickly realize this machine is not like the broaching machines we all know. To start with, our machine is clean as a whistle and quiet as an office copier, and the quality of the broached component is better than was previously thought possible utilizing broaching processes. And the accountant in you will love the savings on both the initial machine purchase and the perishable tooling.

As for the details, the machine is a sturdy fabricated steel structure. The “push and pull” bridge is an extremely robust steel structure designed with “in-line” force transmission to eliminate internal frame and guide way stress and wear. The bridge is guided by two planetary spindles and a vertical (box) rail guide system. A gearbox/brake motor transmits the power through toothed pulleys. A toothed belt and planetary spindles push and pull the main bridge. Synchronous running of the planetary spindles is assured (see figures 1, 2).

The machine can be equipped with one to five broaching stations, although one or two stations are the most common. The scope of part presentation includes a shuttle table, which is activated by means of horizontal pneumatic cylinders. The workpiece is conveyed on hardened ways into the broaching position and back again into the loading position. The part can be placed on the nest manually, robotically, or via conveyor feed, depending on your application preference. Each single station part nest is designed and built for quick “lean” change-out, and independently (tombstone style). The parts may be run in any combination on any station–right, middle, or left side–and changeover between parts should only take one to five minutes.

The broaching operation consists of the part loading, as has been described. Two vertical pneumatic cylinders bring the two bridges together, firmly and accurately holding the broach tools in the upper and lower bridge collets and piloted on the workpiece. The broach tool is then pushed and pulled completely through the part. The air cylinders then expand, allowing the part to be shuttled out. As the next part is prepared, the broach tool is handed off to the upper collet, and the next part can now be loaded (see figures 34). The process is menu controlled from the operator-friendly touch screen PLC.

On top of the push bridge is a special broach-clamping device with a hydraulically activated collet chuck that holds and pushes the broach tool firmly. On the bottom, in the pull bridge, there is also a special broach-clamping device with a hydraulically activated collet chuck, which pulls the broach through the workpiece at the same time. These collets are always perfectly perpendicular to the work nest. As a result, very good guidance during the broaching stroke is guaranteed. The broach can no longer start to vibrate, chatter, or drift off center, as seen in conventional broaching machines. This patented system is what sets our machine apart from all other broaching machines (see figure 5).

In testing at our customer’s facility in South Carolina, the Stenhoj broaching machine improved broach tool life from 2,500 parts per tool sharpening on their old hydraulic broaching machine to 7,500 parts per tool sharpening on the Stenhoj machine, producing parts of a higher quality at a lower cost per part broached. We have seen tool life improvements in every situation where a Stenhoj broaching machine has replaced another broaching machine.

In the Stenhoj design, the “super clean” coolant is 110-percent filtered to 50 microns, and it is then used for two purposes. The high-pressure coolant supply is directed under the broaching table and through an annular nozzle into the cutting tool tooth gullets so that the chips are completely removed. This prevents re-broaching chips and prolongs tool life. It also removes the chips under the table before they can create the problems that many conventional broaching machines encounter with chips in and around the part nest, resulting in scrap and out-of-tolerance parts. The chips and the coolant are passed into a collecting tray, and the coolant and the chips are conveyed out of this tray by the Knoll return oil pump (see figure 6). The “super clean” low-pressure coolant supply is delivered to the exact cutting point through the coolant rings that pinpoint coolant delivery, assuring good lubricity and long tool life.

With nearly 50 Stenhoj machines sold in the last four to five years, the results are clear: This new broaching process produces higher quality parts, at a lower cost per part. According to H. T–nshhoff, Ph.D., who conducted an extensive study of the Stenhoj patented process in 2001, “This push-pulling arrangement balances the forces and provides superior tool life and exceptional part quality.” (The white paper is available on our Web site, listed below.)

Demonstrating value and cost justification for equipment replacement is an easy case for us to make. When considering perishable tooling (50 percent or more savings, typically), machine reliability and lack of down time, and part quality/scrappage issues, a new Stenhoj broaching machine can increase quality, production, and economy. Your setup person will love its simplicity and 60-second tool changeover, your purchasing manager will love the long tool life, and your manufacturing manager will love the dependable, fast, trouble-free operation. And when quoting for new projects, the Stenhoj broaching machine is typically at or below the quoted pricing of old technology using hydraulic machines–a knockoff of a design created back in the fifties.

There are currently eight Stenhoj machines in North America, which have experienced 99 percent up-time availability since initial runoff, and site visits are available. At Stenhoj our customers become our partners in helping us spread the word, and we earn their trust with our commitment to innovative technologies and design.

About the Author
Ken Nemec is national sales manager for Stenhøj Hydraulik at Broachman LLC, which is based in LeRoy, Michigan. He has more than 26 years of broaching experience and can be reached at (231) 768-5860 or ken@broachman.com. Call (231) 388-1402 for a fast quote,
or go online to [www.broachman.com] and [www.stenhoj.de].

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MBA, also known as the “Broachman,” is a card-carrying journeyman broach-maker who specializes in sales and quality process management. Nemec is president of Ever Sharp Tools, Inc. (EST), “where the best broaches on Earth are born, including annulus ring gear, turbine, and hard broaching tools.” To observe the CNC broach tool manufacturing or re-sharpening process or to schedule a visit to your plant, contact Nemec at ken@eversharp.us or go to www.eversharp.us.