Gear Production
Issue link: http://gear.epubxp.com/i/262216
March 2014—17 are usually programmed feed per tooth (f z ) and maximum chip thickness (h ex ). Both of these values should be equal when a cutter is set to a radial cut engagement that is equal to or greater than its own radius. However, the desired chip-thinning effect can only begin to occur when the radial engagement is smaller than the radius. With disc cutters acting basically as gashing or slotting tools in spline manufacture, the small radial engagement in splines compared to the diameter of the cutter means that chip thinning should always take place. In order to get the best possible h ex and optimize a spline "slotting" application, operators must calculate the value of f z , which is derived from disc cutter engagement as related to disc cutter diameter. Consider the formula for chip thinning shown in Figure 1. components between setups for parts with splines. In addition, other features could be machined such as slots, cross holes, fats and more. This fexibility has enabled many shops or Tier- Two suppliers to keep more jobs in-house. Spline operations that had been subcontracted to gear specialists can now stay in the shop—all that's needed is a basic three-axis machining center and rotary table with a relatively small array of disc cutters with indexable inserts. One main advantage of these cutters is the ability to swap out different indexable insert profles on a single cutter body to achieve different whole depths, root confgurations or tip chamfers. Compare that to the necessity of a single hob, spline rack or broach tool with the size and profle suitable only for a single job. Moreover, disc cutters (especially the kind that accept inserts that can be applied to a specifc tool body) are inexpensive compared to hobs, spline racks or broaches. When the need for fewer tools and their ability to machine different kinds of splines are taken together, disc cutters shine as a truly economical choice. Another factor to consider is setup time reduction. For many axle makers, every shaft features a small spline. If a shaft has to move from machine to machine for multiple operations, setup time adds up. The potential for human error in clamping, transporting and re-clamping also goes up. On multitasking machines with disc cutters, these splined shafts can be machined in a single setup. Today's manufacturers are looking for easier component handling with smarter, simpler and more fexible solutions. Repurposable disc cutters and fexible machines are one way to limit tool inventory and control costs for reconditioning, while simplifying workfow and eliminating maintenance headaches. The Chip-Thinning Principle at Work Chip-thinning calculations are essential in effective spline cutting when using disc cutters, as chip thinning is the most basic principle at work in the operation. The two primary feed recommendations from disc cutter manufacturers Figure 1: Determining feed per tooth for chip thinning f z = h ex ∙ DC 2 ∙ √ (DC ∙ a e – a e 2 ) Where: DC = cutting diameter a e = radial engagement Chip thickness (h ex ) is crucial in determining feed per tooth (f z ), which ultimately provides an optimal table feed. If an operator fails to solve for the optimal feed per tooth, there's a chance that the feed rate will be too low for the edge preparation or insert geometry. Because the tool body will provide some tolerance in runout, operators are generally advised to avoid going smaller than 0.003 inch (0.076 mm) in h ex as a rule of thumb. If the value for h ex is too small, a rubbing effect, as opposed to true cutting, can occur. The friction from rubbing produces excessive heat that can eat into tool life and reduce process accuracy. Disc cutter manufacturers should be able to provide maximum h ex parameters. With maximum output in mind, chip thinning is a key consideration in operations that mimic gashing or slotting, such as machining splines 0314_MMS_Gear_MarkFeature.indd 17 2/13/2014 2:44:20 PM