A grinding machine supplier introduced how to use a machining center platform with a vertical spindle for more effective creep grinding.
Peristaltic feed grinding is a grinding process, but more importantly it is not like other forms of grinding. Nelson Beaulieu, Hardinge's grinding product manager, said that in a sense, creep grinding has more of a milling process.
Fig. 1 Let a small diameter grinding wheel be machined using a tool path like a 5-axis machining center
In the final analysis, creep feed grinding is performed using deep cutting and large metal removal methods, which are characterized by the replacement of fast reciprocating movements at a lower feed rate. Creep Grinding Tools - Grinding wheels are machined deep into the processed material just like milling cutters.
In fact, when the diameter of this tool is reduced and close to the diameter of the largest milling cutter on the typical machining center, it can show its higher efficiency. Beaulieu said that if the machine itself is designed like a vertical machining center, then such tools will show higher practical benefits.
Mr. Beaulieu said that the idea behind his company's grinding machine based on the VMC vertical machining center is behind this. The FGC Type 2 "Flexible Grinding Center" offered by Bridgeport (affiliated to Hartinge) deviates from the traditional creep grinder design, where the orientation of the main shaft may represent an essential difference.
Figure 2 The surface of the blade is processed using a creep grinding process.
During grinding, the rotary axis of the machine feeds along the arc of the part.
Different processing methods
Mr. Beaulieu said that when the creep grinding process was first developed, virtually all grinding machines used horizontal spindles. Creep grinding processes natural building on the basis of this platform. However, one of the basic requirements of this horizontal design is the need to use a very large diameter grinding wheel. Its diameter is large enough to allow the edge of the grinding wheel to reach the worktable to facilitate the removal of the mainshaft cover.
Mr. Beaulieu also stated that this requirement will have certain limitations. For efficient creep grinding, the permeation of the coolant is critical, but the wide curvature of the large-diameter wheel will cause its space to shrink, affecting the penetration of the coolant. In addition, large diameter grinding wheels cannot be interpolated along complex machining paths. For this reason, parts often need to use complex fixtures to clamp. Because the parts being ground have different characteristics, when they are moved from one creep feed machine to another, the parts also need to be changed from one fixture to another.
On the other hand, if the main shaft housing can be removed from the work area, it is advantageous to apply a smaller diameter grinding wheel. As a result, the coolant can also be delivered directly to the machining section more efficiently, allowing the part to be fed through the rotary axis, allowing the small-diameter grinding wheel to be machined using the tool path like a 5-axis machining center.
In essence, the FGC machine is actually a 5-axis machining center. However, because the workpiece uses grinding instead of milling (in the ordinary sense of milling), the machine tool must have some degree of rigidity, that is, the key strength that has to be a traditional horizontal platform. Unlike the typical VMC vertical machining center, its rugged, solid cast iron base weighs 30,100 lbs. Also unlike vertical machining centers, they need to be used in combination with a dedicated coolant system because during creep grinding the system is required to deliver 1000 psi (lb/in2) or 50 gal/min flow. The coolant.
These changes mean that the use of a vertical machine does not require very expensive initial costs. Mr. Beaulieu said that once such machines are used, they can immediately save money. Its sources of savings include the following:
(1) Less fixtures and machine tools. It is not necessary to commission the cards several times. Only one-time loading of cards is required to complete all grinding tasks.
(2) Shorten the commissioning time for workpieces, because no complicated fixtures are required;
(3) The processing operation is reduced, because the same grinding wheel can be used to change the direction of the parts in the production cycle and process different parts separately;
(4) The processing speed is increased (its fund saving degree exceeds the savings of the workpiece debugging and carding) because the smaller diameter grinding wheel can work more flexibly. Mr. Beaulieu said that on this machine tool, the user only needs to use a lower depth of cut to obtain a higher metal removal rate, because the potential feed rate is much higher than the actual speed.
Figure 3 The machine is used in combination with a dedicated cooling system (the system is located on the left side of the machine),
It can deliver the high pressure and high flow coolant required during peristaltic feed grinding.
Traditional processing
If the machine tool is used completely in accordance with the traditional VMC vertical machining center, further savings can be made. The spindle uses a standard BT interface for the machining center tool, and its grinding wheel is connected to the spindle through a standard machining center tool changer. Therefore, the same system can be applied to more typical machining centers within the same machining axis cycle. This means that the cutter or drill can be waiting in the magazine next to the grinding wheel for ready use. If a milling or drilling process is required on a certain grinding surface, the workpiece can still be in the same clamping state for the machine to perform such additional machining tasks.
In order to make the processing platform of the VMC vertical machining center more easily applied to creep feed processing, another method can be adopted. This method has a close relationship with the resources outside the work area. Because the machine tool used is so similar to a standard machining center, it enables the operator of the machining center to efficiently program and perform peristaltic feed machining operations, thereby improving the machining capability of the machine tool. As Mr. Beaulieu pointed out, "The number of milling operators available is greater than the number of grinding operators."
Why creep feed grinding?
Mr. Beaulieu said: “If all processing can be solved by milling or broaching, then we are very willing to accept.†Creep processing is a challenge to other processing processes, because there are some problems with these other processing processes. Creep processing has the following advantages:
(1) has excellent processing characteristics. This kind of grinding process can absorb a part of the heat in machining cutting. Especially in the processing of titanium, Inconel and other materials, it is more effective, mainly because the heat generated during processing will accelerate the wear of the cutter or broach;
(2) Maintain a good surface finish. This grinding process does not require excessive pressure on the machined surface, but the ability to grind materials is high, while maintaining good surface finish and perfect surface finish quality;
(3) No glitches will occur. The use of this grinding process does not require burrs;
(4) The inherent accuracy can be maintained. Under well-designed process conditions, milling and broaching can indeed achieve high machining accuracy. However, with a well-designed grinding process, even higher machining accuracy can be achieved.
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