Grinding Journal - Fall 2007 - (Page 17)

Methods must be matched to the application To achieve maximum productivity, however, grinding methods and technology must be matched to the specific manufacturing situation at hand. By outlining the primary variables in the grinding process, then analyzing the benefits and limitations of different grinding technologies relative to those variables, we can get a picture of which methods are best for certain applications. Let’s consider five key variables in the grinding process: make up another crucial variable affecting a shop’s overall grinding strategy. Issues include the part’s shape (geometry), material and possibly coating, and tolerance and surface finish requirements. Engineers often design complex superalloy parts and then expect a shop to find a way to produce the design. Some delicate components require special attention to avoid distortion from excessive grinding or clamping forces. And of course, part tolerance and surface finish requirements heavily influence the grinding process and abrasives that are chosen. Investment: The most conspicuous variable of any grinding operation is the capital investment required. A shop must determine whether it needs a full 5-axis machine with tool changer, or if a simple 3-axis machine will suffice. The coolant system, critical to the grinding process, is another major investment. Even floor space is a cost factor, taking into consideration the size of parts and machining equipment involved. Workholding: Finally, in what is in some respects a subset of part design and investment considerations, we must consider the workholding variable of the grinding process. Workholding choices can include methods from hard point tooling to encapsulation of the part being ground. Fixturing costs can sometimes outweigh the cost of the part due to complexity and extra support requirements. We’ll use these variables to evaluate the benefits and limitations of four different combinations of grinding methods and technologies, each based on case studies. We’ll also use a “Q-Prime” measurement to compare the metal removal rates of the various grinding techniques. It represents the volume of metal removed per unit of time and provides a basic rule-ofthumb for measuring metal removal rate in grinding. It’s typically expressed in cubic millimeters per second (mm3/sec). Strategy: A second variable is a shop’s prevailing manufacturing strategy. Strategic approaches may include a lean production or single piece flow, where a part moves from machine to machine; or an automation approach where tool changing and other technologies permit completing a part on one machine; or a job/prototype shop focus, tailored to provide flexibility to meet constantly changing customer demand. Environment: The environmental variable in grinding is increasingly important. Part material and configuration as well as the grinding process itself determine whether oil- or water-based coolant systems will be applied. The choice involves weighing benefits and limitations including disposability, cleanliness, and fire precautions. The amount of material removed and grinding wheel consumption also are environmental considerations. The four grinding methods and technologies we will discuss are: Design and tolerances: The design and tolerances of the part being processed 1. Conventional creep feed grinding 2. Creep feed continuous dress (CFCD) techniques 3. Using vitrified CBN (cubic boron nitride) abrasives 4. Using plated CBN wheels Grinding Journal 17

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Grinding Journal - Fall 2007 Contents From Virginia: Apparently no credit crunch for machine tools Why measure cutting tools Other perspectives on CNC tool measuring Productive grinding of superalloys SUPER service grinding BIG rolls Problem Solver

Grinding Journal - Fall 2007

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