High precision grinding various shapes permanent ferrite

High precision grinding permanent ferrite product had been a vacancy in China permanent ferrite industry. It was caused by the low attention paid for several years since the selling price was low, applicable tolerance was large and low requirement for product precision. Most of the grinding machines selected by permanent ferrite enterprises are coarse equipments, which cause the ground products with a tolerance of ±0.5mm. With the continuous developing of permanent ferrite market, many countries and areas like Japan, American and Taiwan area have moved their factories to China. Many users abroad come to China to buy permanent ferrite and China has become one of the largest manufacturers of permanent ferrite in the world. Many orders with high precision grinding requirements come to China one after another, however, since the lacking of high precision grinding equipment, permanent ferrite manufacturer feel hard to handle them.

To meet the marketing demands, many grinding equipments with high precision, high efficiency and high automatic level are designed. Many different types of grinders are designed to grinding different shapes, sizes and specifications ferrite products, especially, the multi-working position arc grinder specializes in grinding various arc magnet, automatic feeding double face grinder specializes in grinding end sides of thick or thin small ring, high precision multi-position coreless grinder specializes in grinding outer circular of cylinder magnet, high precision multi-position coreless grinder specializes in grinding outer circular of thick or thin small ring magnet, double face grinder specializes in grinding height of double end sides. So many special equipments ensure the permanent ferrite manufacturers to extend market range, enlarge market shares, advance product quality, lower production cost and advance economy efficiency.

High precision arc grinder grinding technique and equipment

Arc grinder is specially used for processing arc magnet. So far many countries in the world manufacture arc grinder including Japan, America, Italia, Sweden and Romania. The grinders they manufacture differ from structure. The grinding heads of arc grinders manufactured by Japan, Sweden and America adopts vertical separation passing way, only the structure of their feeding and grinding heads are different. While only Italia and Romania adopts horizontal separation passing way for their grinding heads. Analyzing the structure and grinding theory of various arc grinders overseas, we can see that the vertical passing way is better, which can grinding the highest precision products. Horizontal passing way is hard for us to control grinding precision according to our current sintering roughcast.

So the grinding head of arc grinder manufactured by us are designed with vertical separation passing way, it refers to the frame structure Japanese arc grinder. That is to say, set grinding wheel apart from feeding line and grinding axis, but we choose the whole cast frame structure instead of Japanese angle iron frame structure. The weight and hardness of our grinders are far more than Japanese. The super strong hardness counteracts the shake during grinding arc magnet and builds a stability foundation for high precision grinding arc magnet.

We design a special automatic feeder on automatic feeding machine, which solves the low efficiency of manual feeding and reliability problem of auto feeding.

The grinding structure we design adopts vertical separation structure, which means that the grinding head is for single side grinding, another side is benchmark, so it ensures the precision on grinding process.  We choose super hard material to make gliding parts of feeding line to ensure the rail won’t be hurt when carrying arc magnets.

In spindle structure, we adopt our high precision water-cooling grinding head and use cool water cycle generated by grinding and cutting to cool grinding head in working process, which resolve the radiation problem when grinding head running bearing continuously works and ensure the  24 hours running high precision for diametrical oriented jumping and axially oriented moving of spindle.

The heavy cast structure applied on the grinding head ensures the high stability of grinding. Elector raster location with digital system applied on transmission structure of grinding head with manual and electric structure facilitate up and down movement and adjusting of grinding heads before and after.

In grinding head quantity structure, we have base type which are two-position (double grinding heads) and three-position (triple grinding heads) and combined type. By connecting two sets two-position, we can get a four-position, by connecting the two-position and the three-position, we can get a five-position, in the same way, a six-position can be got by connecting two sets of three-position.

When changing product type, it is convenient to replace the feeding tire and adjust feeding railway.

In grinding specification, we have two types: the minimum type can grind product with 7mm chord width and 1mm thickness, the maximum type can grind product with 150mm chord width and 40mm thickness. If necessary, the one to grind super large arc magnet with 200mm chord width and 50mm thickness can be designed.

The grinding practice proves that in order to grind ideal high precision and smooth finish products, besides installing high precision grinding head as core part, the multi-working position arc grinder should be configured with high precision grinding wheel and correct grinding technique. So the dimension tolerance of arc magnet would reach ≤ ±0.02mm.

High precision multi-work position centrifugal grinder

The most common products we can find on micro motor rotor are cylinder magnets and ring magnets (including thin and thick wall types). The outer circle of sintered roughcast needs to be processed by rough grinding and fine grinding. Normally, universal centrifugal grinder was adopt to process cylinder, thick and thin wall rings, which would cause the low efficiency, large taper tolerance, low consistency and other quality problems.

Based on this phenomena, we find the reasons to cause the low efficiency and bad quality by further research and analyzing:

  1. The centrifugal grinder is single grinding head structure and it needs 2 sets of grinder to grind cylinder roughcast twice.
  2. Manual feeding in grinding process will cause intermittent grinding and material intermittent stay between grind wheel and idler pulley, so the size would be smaller, ellipse or triangle.
  3. Worn guide is not replaced in time.
  4. The central height of guide is not adjusted, too high or too low.
  5. The precision or the centrifugal grinder is not correct and cannot be adjusted to the factory precision. Even new grinder will have precision problem when using in one year or more.

Based on the reasons mentioned above, we desert traditional centrifugal grinder structure and adopt new design thought—resolving all problems via structure:

  1. Adopt two-working position or three-working position structure to design grinding head, which means to install 2 teams or three teams of grinding heads on the same grinder, feeding once, process rough grinding and fine grinding or process rough grinding, semi-rough grinding and find grinding continuously twice or three times.
  2. Specially designed carrier and feeder for feeding machine ensure continuous grinding process during carrying and feeding, it reduces intermittent grinding and increase product grinding quality and size consistency.
  3. The principle axis structure of grinding head is the core of the whole grinder, the grinding head structure adopt double-headed bearing, load-bearing and water-cooling structure, the reason that we do not adopt universal centrifugal grinding head half-arc bearing structure is that the copper arc bearing of the principle axis is easy to worn, especially when grinding large quantity, which is not suitable for ferrite permanent magnetic materials. So, the gap of principle axis copper bearing tends to become great, which will lead to the principle axis loosening and noise. At this time, the factory need to take a hard job and spend much time to amend it. Because amending the copper arc bearing needs professional, normal factory can’t do it. The only way is to send the grinder to its manufacturer. That is a popular problem exists in ferrite factory. The new principle axis structure we design is a gravity-type structure for grinding large quantity, its principle axis box is super-heavy type, the principle axis is super-width diameter or super-length.It ensures that the grinding force is more powerful than its counterforce. So you can feel the powerful force from grinding head while the voice and shake are gentle from running. It is easy to grind roughcast with high precision. You can recover the grinding precision by replacing the worn principle axis.
  4. For rough grinding, the copper based diamond grinding wheel should be chosen. For fine grinding, resin diamond grinding wheel can ensure the grinding efficiency and precision.
  5. For idler pulley, we adopt the latest variable frequency motor and adjust idler pulley speed by transducer, which resolves the high failure rate by using electrical-magnetic motor and advance reliability of using centrifugal grinder.

In addition, a whole new design for guide block makes it simple structure, convenient to adjust, firmly clamping and high reliability. In the design for guide, we adopt a guide with height adjustable, which highly advance its using life and reduce the cost. Considering the effect to grinding quality by guide, we adopt excellent material and using high speed steel blade to machine guide to ensure its hardness and tenacity and advance its wear-proof.

Grinding practice prove that by adopt this grinding technique and grinder, we can produce cylinder magnet with the circle tolerance within ±0.01mm and the ring magnet with its circle tolerance within ±0.01mm and the taper tolerance within ±0.01mm.

Double end sides grinding technique and equipment for small or thin wall ring magnet

With the developing of application market, many small motors adopt permanent ferrite magnetic ring, especially the thick ring and thin wall small ring. The non-verticality requirement of magnetic ring for micro motor is very high. To ensure the precision of non-verticality, two conditions are necessary: First is the plane tolerance of both end sides should be kept within ±0.01mm, secondly, the tolerance of non-roundness and taper tolerance should be kept within ±0.01mm.

How to bulk produce high precision end sides small ring magnet?

It is well known that small ring magnet is hard to machine with regular equipment due to its large quantity, small diameter and thin wall. So we design disc type automatic feeding double end-face grinder.

Referring to grinding technique, following conditions should be met for grinding small ring magnet:

  1. High precision grinding head
  2. High precision verticality when grinding
  3. Rotation speed should be fixed when grinding ring magnet end sides
  4. Rough grinding and fine grinding should be separated
  5. Full automatic carrying, feeding and grinding to realize bulk production and high efficiency

Below parts should be take full consideration based on the technique requirements of grinding small ring magnet:

  1. The precision of grinding head should be designed to keep its radial flop and axial move tolerance within ±0.0025mm
  2. Strict requirements for grinding technique to make sure the grinding position precision
  3. The lifting board for grinding is designed with a semi-circular hole to ensure ring magnet rotate under a fixed speed when grinding
  4. The final process of fine grinding should ensure the remainder within 0.05mm (double sides)
  5. Special automatic feeding design can make thousands of ring magnet line up and enter disc feeder with fixed speed for grinding

Thousands of grinding practice prove that adopt this grinding technique and grinder can keep the parallel tolerance within 0.01mm and end-side tolerance within ±0.01mm, The producing efficiency can reach 1m~3mm per minute. The precision of end-side size ensures a precise flat benchmark when grinding outer circle with centrifugal grinder and only through this, the non-verticality requirements of small ring magnet and thin wall ring magnet can be met.