Achieving Squareness and Parallelism
At its most basic, precision surface grinding services are used to achieve two things: to make cubic shapes of metal square and parallel to as precise as the machine performing the grinding is capable. Used for many things, but typically fixtures, molds,and dies, surface grinding seems like a simple process at first glance. But look deeper and you find that there’s more to mastering surface grinding than meets the eye.
Applications for Precision Surface Grinding Services
For six-sided cubic rectangular or square pieces of metal, precision surface grinding enables you to make each side square and parallel to itself or a reference surface. These square or rectangular blocks are usually held in place on the grinding table by magnets, so that you have one flat surface against another flat surface. From that critical foundation, surface grinding can then be invaluable for applications such as die manufacturing. The positional accuracy required by dies used in extrusion and injection molding means the dies must be square to the outside of the center, and it is here that precision surface grinding delivers. You simply cannot mill a block of metal as squarely and precisely as you can with surface grinding — not to mention, the milled surface will never match the ground finish for a low Ra value.
Precision surface grinding services can also be used for round rod. Although the outside diameter of the rod is not made round by surface grinding, the two ends of the rods can be precision surface ground to make them perfectly perpendicular to the outside diameter. Here, V-blocks are employed to position the rods for grinding. The round rod is placed into the V-shaped cavity, and a clamp holds the rod vertically in place. From there, precision surface grinding can be used to grind the top of the rod to a dimension that is perfectly square to the outside diameter.
The X-Y-Zs of Surface Grinding
Although there are manual surface grinding machines, a critical feature of the surface grinding process is the precision repeating removal of small increments of material, where the less you remove, the better the surface finish and the better the dimensional accuracy. It is not advisable to remove a lot of material thickness in one pass, because it will produce a bad surface finish and because that type of stress on both the metal and the machine can result in poor positional accuracy. Rather, it is far better to make many, many repetitious passes, with each one removing slightly more material. Watching automatic surface grinders is like seeing a perfectly choreographed rapid-repeating motion where each intervals is imperceptibly moving just a little farther along. The machines in a row slide side to side with none of the vibration and noise that accompanies metal removal by turning.
The usual standards for precision surface grinding services are also the principles of motion that drive the grinding table, with one difference — the horizontal X axis action that provides the side to side repetitions and the Z axis grinding action that provides the back and forth passes. Sophisticated precision surface grinding machines have automatic Z axis, allowing for the tiniest of increments to be applied to the workpiece with each of the X axis repetitions. Yes, you read that right — in the world of surface grinding, the vertical direction is the Z axis, whereas in milling that is called the Y axis.
And then there is the Y axis. On precision surface grinding machines, typically the wheels are not as wide as OD grinding or centerless grinding wheels. The benefit of the Y axis motion is that it allows a 1” thick wheel to precisely grind flat a surface that is more than 1” wide. In fact, workpieces can be many multiples wider than the grinding wheel. With each repetition of the X axis, the Y axis is moving ever so slightly to produce the specified flat surface. And while there are many different sizes of surface grinders, the same X-Y-Z principles apply.
Feed and Speeds, Wheels, and Coolants
Although the principles of precision surface grinding services seem simple, the practice of surface grinding requires years of experience and expertise because there are many subtle variables. As with all skilled and productive machinists, surface grinding experts critically need to understand the behavior of different metals as well as the variables of feeds and speeds, wheels, and coolants.
In the case of precision surface grinding services, feed refers to the rate of the three axes. Arguably, feed is the major deciding factors for achieving the desired surface finish. Speed refers to the wheel RPM, though interestingly in surface grinding, wheel RPM is usually constant.
With wheels, the opportunities to choose the perfect wheel are as wide as the selection and variety of wheels that are available. However, expertise comes in knowing the limited number of optimal wheels for each of the many different types of metal comprising the workpiece. Similarly, through years of experimentation and commercial practice, there are only a few desirable coolants. However, as with all other machining processes, the way coolant is introduced to the surface grinding process remains an important method to get right.
Together, these four variables are the primary drivers of the surface finish that precision surface grinding machines will produce
Expertise in This and More
Like many professional disciplines these days, the world of precision surface grinding services has many subspecialties. Beyond the simple tasks of working a cubic shape or the ends of a shaped part, there are many permutations that can be achieved using different attachments, as well as many techniques and CNC-driven capabilities to the robust standard surface grinding machine. For example, these machines can be fixtured to make forms, corners, or chamfers, or to even do cut off, and fully rounded radiuses are possible. All of these shapes are known more specifically as form grinding or profile grinding.
The icing on the cake is that as a precision metal fabricating company, Metal Cutting is highly experienced in not only surface grinding of six-sided cubic shapes and the ends of cylinders, but also these other disciplines — making tight tolerance parts in many different shapes using the combination of our precision grinding wheels and our expertise.
Give Metal Cutting a call for precision surface grinding services and your other small metal parts needs. And for helpful tips on how to create specifications that will produce the results you’re looking for, download our white paper How to Fine-Tune Your Quote Request to Your Maximum Advantage: Frequently Asked Questions in Small Parts Sourcing.