1、14FTM01 AGMA Technical Paper Molecular Decomposition Process = Electrochemical Assisted Precision Form Grinding By J.A. DeAngelo, Oberg Industries2 14FTM01 Molecular Decomposition Process = Electrochemical Assisted Precision Form Grinding Joseph A. DeAngelo, Oberg Industries The statements and opini
2、ons contained herein are those of the author and should not be construed as an official action or opinion of the American Gear Manufacturers Association. Abstract Super-finishing of forms, required to generate geometry like that of the involute of a gear, is a multistep process where gear blanks are
3、 roughed, heat treated, ground to precise tolerances allowing for additional stock removal to occur in another value added process to generate super-finishes to less than 1 Ra in. A solution that enables the rough and finish grinding to occur that produces super-finished surfaces to less than 1 Ra i
4、n while maintaining precise geometries is Molecular Decomposition Process (MDP). MDP is an anodic dissolution process (electrochemical) whereby the work piece is the anode and the grinding wheel is the cathode. Specific controls of electrical, mechanical and chemical actions are applied to enable th
5、e MDP system to remove stock without mechanical or thermal deformation. This process enables stock removal rates in sample materials such as nickel and titanium alloys to occur at rates more aggressively than conventional creep-feed grinding. For example: stock removal rates expected by creep-feed g
6、rinding in titanium and nickel alloys are at a rate of Q = 20 mm2/s. With applied MDP technology and standard aluminum oxide abrasives, cut rates achieved in nickel alloys (Stainless and inconels) are recorded Q = 57 mm2/s. Cut rates for titanium alloys are recorded at Q = 29 mm2/s. Alloy steels whe
7、n exposed to MDP illustrate stock removal rates typically 5 times faster than conventional grinding means. Applying super-abrasives to the system greatly increases the rate of stock removal and perishable life. The anodic process implemented permits the perishable wheel geometry to be preserved whic
8、h equates to longer perishable life and dimensional stability, which enables longer production runs with consistent dimensional results. Surfaces generated by the applied MDP technology, as reviewed at scanning electron microscopes (SEM), clearly illustrate no evidence of plowing tearing or smearing
9、 of the base material. This reduced mechanical force at the surface of materials being exposed to the MDP technology yields improved surfaces. Appropriately defined processes have reproducible results of surface finishes to 1 Ra in or better. In addition, while these reduced mechanical and thermal f
10、orces allow for the product to be produced with super finishes, another benefit of the MDP system is a burr free component. This assists in reducing the number of steps required to produce a completed gear or component. The MDP system is designed and operated to ensure the inputs of power, perishabl
11、es, electrolyte, and motion are monitored and maintained, as to provide consistent outputs that are illustrated through finished product. These controls are refined to ensure dimensional accuracy is one of the major outputs of the process. These same controls allow for the MDP process to be maintain
12、ed as an environmentally friendly process. It is worth noting that typical anodic processes can be a hexavalent process. The MDP system is designed and confirmed not to generate byproducts that are unfriendly to operator and the environment. These controls add stability to the system that equate to
13、extended perishable life for both abrasive wheels and electrolytes used within the system. MDP has proven to produce gear involute geometries from “as supplied” blanks with minimal stock for finishing. Roughing and finishing of forms in full hardened alloy steels such as 4140 tool steel yielding an
14、MDP produced product with surfaces to less than 1 Ra in while maintaining dimensional stability to achieve a 1.67 CPK. The MDP system removes large or small amounts of stock while providing a safe work environment for operators and the environment. MDP is electrochemical assisted precision form grin
15、ding. Copyright 2014 American Gear Manufacturers Association 1001 N. Fairfax Street, Suite 500 Alexandria, Virginia 22314 October 2014 ISBN: 978-1-61481-093-3 3 14FTM01 Molecular Decomposition Process = Electrochemical Assisted Precision Form Grinding Joseph A. DeAngelo, Oberg Industries Introductio
16、n Molecular decomposition process is an electrochemical grinding process that has been refined to enable: - The removal of increased amount of material while maintaining workpiece temperature to within 1F. - Reduced mechanical force to the workpiece. - From roughing operations surface finishes achie
17、ved measure at 6 to 8 Ra in. - Finishing operations are able to achieve surface finishes of 1 Ra in or less. The MDP can be outlined as follows: - Isolation of workpiece and spindle from balance of equipment. - Power supply design to address power surges or brown outs from external power sources. -
18、Electrolyte management system that cleans particulate (anode mud) separates particulate from the balance of electrolyte through controlled filtration maintaining uniform electrolyte conductivity. This filtration process provides a valuable benefit in the elimination of heavy metals such as arsenic a
19、nd hexavalent chrome (making the designed system environmentally friendly). - Electrolyte formulation specifically maintained to assist the total system. - Controls of perishables through specific wheel formulation designed to address, conductivity, resistance, abrasive type and concentrations of ab
20、rasives. - Within the operation of the MDP system, wheel life is increased requiring less time in dressing particular forms within the perishables thereby increasing the spindle time in the area of part production. - Combining all of the actions within the system is done through controlled algorithm
21、s that enable operation of the MDP equipment to happen in the background. This permits operation of the MDP equipment from any level of expertise. Within the MDP system the workpiece is isolated from the balance of the equipment and power is passed through the conductive workpiece making the workpie
22、ce the anode within the MDP system. The isolation of the spindle and conductive “Voltron” grinding wheel are employed to enable the grinding wheel to be the cathode within our electrochemical cell. See Figure 1. Through the anode to cathode relationship a defined material removal through a deplating
23、 action is present within the electrochemical cell which seems to soften the material for stock removal and at the same time prevents softer alloys from adhering to the cathode (conductive grinding wheel) allowing for a clean free cut of material without mechanical or thermal damage. Surface finishe
24、s resulting from the MDP process are improved through the ability to maintain uniform cutting action. Within conventional grinding and machining processes the tools utilized to perform the work introduce the largest potentially uncontrolled variable. Within a machining operation tools wear from the
25、initial moment the cut edges are exposed to the alloy being removed. Efforts to enhance cut edge life require extensive engineering for cutter material, coatings, rake and cutter geometry all efforts to enable longer life through the cuts. Similar engineering efforts are performed for abrasives util
26、ized within grinding wheel production to enable open clean cuts through porosity of the wheel or high pressure coolant systems that assist in keeping the abrasive wheel free of alloys or debris being ground. In either case, a dulling of the abrasive or cut edge translates to mechanical observations
27、at the surface of the alloy being exposed to the stock removal process that would typically be referred to as tearing plowing smearing, or sliding of material. Figure 2 illustrates many of the conditions which can directly impact the final as machined / ground surfaces. The cutting process being the
28、 desired action between an abrasive and a work piece (1.1) Balance of conditions illustrates a level of mechanical deformation at the surface that leads to increased friction (heat into the work piece). Abrasive stock removal reflected within (1.3 through 4) are conditions that are least desired tha
29、t prohibit dimensionally accurate stock removal. MDP prevents these types of conditions. 4 14FTM01 Figure 1. Illustration of isolated work piece (anode), Voltron grinding wheel (Cathode), filtered electrolyte delivery between the interface of the Anode and Cathode (work piece and conductive wheel) F
30、igure 2. The cutting process being the desired action between an abrasive and a work piece 5 14FTM01 The dulling effect of the cutter or abrasive is best illustrated as reviewed through a scanning electron microscope (SEM) of the surface of the alloys. Figures 3 and 4 are SEM images of conventional
31、ground verses MDP ground product. (Note: alloy illustrated within Figures 3 and 4 maintain the same certifications as they are both from the same bar of stock). Figure 3 is conventional ground alloy with a 180 grit diamond abrasive. Ripping tearing and smearing are all present within produced sample
32、. Figure 4 is MDP ground alloy with a 180 grit diamond abrasive. Linear lines present are direct translations of geometry that is present on the face of the 180 grit diamond grinding wheel (cathode). Benefits of the MDP system are that of true geometry and material characteristics are present at the
33、 surface of the work piece. Any geometry present on the surface of the perishable wheel directly translates to the surface condition on the work piece. When super finishing of specific geometry is being requested, the perishable wheel is the first item that must be produced with a uniform desirable
34、surface finish and geometry. The perishable wheel and the grind approach must be one that will permit the removal or uniform blending of the surfaces through mechanical action or geometry. It is fair to state that if the perishable utilized within the MDP system has a measured Ra this will directly
35、impact the final Ra of the work piece. Within conventional grinding, this level of detail is easily discarded as the change of cut condition and the presence of smearing and tearing are ongoing through the process. Figure 3. Conventional grinding conducted with 180 grit diamond abrasive at a field o
36、f view of 25 m Figure 4. MDP grinding conducted with 180 grit diamond abrasive at a field of view of 25 m 6 14FTM01 Adapting the MDP process to gear grinding Achievable surface finishes of a system are a result of multiple inputs including, accuracies of equipment (mechanically and thermally), life
37、of the perishable tool, and repeatability through the entire geometry generation or linear inches of grind. Gear production is typically performed by a roughing process (broaching or machining) heat treatment, grinding operations, gear form grinding, when required, super-finishing is achieved by rot
38、ary tumbling with some media and chemistry (mechanical polishing). The value added process of rotary tumbling requires dimensional planning with specific focus on the amount of material removed by that value added process, where the material is removed from and which zones are subjected to more mate
39、rial removal during the polishing process in order to generate the required surface finish. Once defined, these processes are predictable and repeatable and become part of the process flow. Wheels/perishables Cubic Boron Nitride wheels within conventional grinding systems require precision made hubs
40、 that are manufactured to matching geometries for the desired profile. These metal hubs are then plated and the super abrasive is layered onto the precision hub which is subsequently dressed and measured to ensure uniform geometries are achieved. Aluminum oxide and silicon carbide wheels can be dres
41、sed within the gear grinding equipment utilizing programmable paths or formed dressing wheels. Dressing of these wheels within the gear grinding equipment delivers the desired profile with the geometric accuracies of the equipment directly translated to the perishable and subsequently to the product
42、 being ground. When grinding multiple teeth, multiple passes and multiple dresses of the perishable may be required within the conventional grinding system to produce uniform geometry. Whatever the abrasive selection within the MDP system, the benefits of producing the conductive wheel is the first
43、item that increases the overall ability of the perishable to maintain uniform geometry through the required linear inches of grind. Abrasive selection is more to enhance the overall life of the perishable to the number of form dresses that would be required for a desired form. Although wheel life is
44、 product specific, testing conducted has illustrated 5 to 10 times longer wheel life within the MDP systems as compared to conventional grinding systems. Applied MDP process benefits Increased wheel life is a benefit from the applied MDP technology. This increased wheel life enables uniform geometry
45、 for roughing to finishing with less expensive types of abrasives while maintaining required dimensional attributes. The increased wheel life and less expensive abrasives has an added benefit of enabling a gear grinding system to rough stock from a solid form within a single setup of the MDP interfa
46、ced equipment. Conventional grinding system utilizing a plated CBN wheel is less desirable for this approach due to the resultant mechanical and thermal stresses that would be generated within the product, along with the expense of the plated CBN wheel. Accuracy and repeatability are achieved within
47、 the MDP perishables through the use of accurate and repeatable tool mounts. These accurate tool mounts enable the offline dressing of precision forms and provide repeatable accurate geometries. This method of form generation consistently provides uniform surfaces onto the form geometry of the peris
48、hable that would normally be viewed as grinding lay that subsequently affect the surface finish of the work piece. Controls of the perishables through abrasive size, conductivity, and concentration further enhance the MDP process. As the grinding wheel is the cathode within our electrochemical cell,
49、 the abrasives are present to assist in the removal of non-conductive elements. The electrochemical action grinding swarf is a fine particulate (anode mud) that does not adhere to the perishable during the grinds. This enables finer abrasives to be utilized for increased levels of stock removal. Due to the finer meshed abrasives and refined dressing techniques, a uniform and consistent surface is generated onto the form of the perishable wheel. The extended wheel life gained from the applied MDP results in an improved surface of the form being ground with the applied M
