Spring Grinder Machines

 

The method most commonly used places the springs in a feed plate that captures the spring on its diameter and holds it upright. This feed table hole or bushing is normally 0.008-0.010 inch larger than the spring OD and 80-90% of its free length. The feed plate then forces the springs between the two grinding stones.

The springs are loaded into the feed plate one at a time, by hand. Though I have seen this operation modified to use an automated feed. Normally this is only done for extremely high volume jobs as the changeover time from part to part can be quite lengthy and difficult.

The above automated feed operation is only used on what is called a crash type or crush type spring grinder machine. This type of grinder has the two opposing grinding stones set to grind the spring to the finished length. The feed plate forces the springs to crash into the stones and then they are crushed down between the stones with the load of the spring pushing the ends of the spring into the stones. When the springs come out from between the stones the springs are at the finished length needed.

The crash spring grinder machine has two common types. Usually it comes as a single head(two opposing grinding stones) or a tandem head(two sets of opposing grinding stones).

The single head crash grinder is good for a reasonable squareness of 2 degrees or better. With a very good setup even 1.5 degrees can be reached.

A tandem head machine can reach 1 to 1.5 degrees much easier than a single head machine. Productions speeds are also faster. This is accomplished by grinding approximately 80% of what is required in the first set of heads (rough heads) and finishing the final 20% in the second set of heads (finish heads).

However, the cost of the machines, the tooling cost, and setup times are greater than single head spring grinder machines. For this reason these machines are usually used only on very high volume work.

Downfeed type grinders are also called CNC grinders. In the downfeed type grinder the top grinding stone is not in a fixed position. It has a starting position and a finished position. The bottom stone is set at a fixed position.

The top stone travels at a controlled rate of speed toward the lower grinding wheel. While this is happening the feed table makes multiple high speed passes between the grinding stones. The top stone stops its downward movement at a set point that is normally the free length of the ground spring. At this point the feed table makes a few more passes (called the sparkout phase) to put the finishing touches on the spring.

Downfeed grinding allows the spring grinder to apply the maximum amount of grinding pressure on the springs without buckling them in the grinding fixtures. This helps keep the parts square.

Here is a downfeed grinder going through its cycle:

A typical downfeed grinder can hold a squareness of 1 degree or better. Also, free length variation can be minimized greatly with the correct setup technique, use of grinding pressure, and final sparkout.

The rate of downfeed discussed above, the finished set point, the spark out time and many other features are controlled by a computer and servo motors. Of course these items vary from machine type and machine maker, but the basic concept is the same.

Let it be known that the accuracy of the finished quality of the springs coming off any type of spring grinder is inherent upon the quality of the spring coming from the spring coiling machine. Excessive variation in free length from a coiling machine will result in excessive scrap on the spring grinder.

The machines we’ve discussed above are the most commonly seen in today’s spring manufacturers. There are other types of spring grinders used by spring makers. There are tub grinders that use a single grinding stone on the bottom that grinds one end of the spring at a time. There are also the horizontal type double end grinders which are sometimes called Ferris wheel grinders because the feed plate is upright and carries the springs through the grinding stones like a Ferris wheel.

Find out more details by going to our page on SPRING MACHINE SUPPLIERS to see what is being offered by the grinding machines manufacturers.

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