Hydraulic Cylinder Manufacturing

Hydraulic Cylinder Manufacturing

Hydraulic Cylinder Manufacturing

With the industrial revolution, fluid power began to be used in many industries. Today, fluid systems; It has become an indispensable part of every field from agriculture to metal industry, from automotive to aviation industry. Hydraulic cylinders, one of the most important parts of liquid fluid systems, provide linear movement by converting hydraulic energy into mechanical energy. Hydraulic cylinders are also called hydraulic linear actuators because they provide linear movement.

In this article, the manufacturing of a sample hydraulic cylinder will be discussed and examined in detail to give an idea about hydraulic cylinder manufacturing. In the sample cylinder design, tips will be discussed with the “design for manufacturing” (DFM) mentality. First, exemplary hydraulic cylinders and their parts will be presented. Then, the production tools to be used will be discussed. Finally, the parts and the manufacturing process will be examined step by step with design for manufacturing (DFM) details from start to finish.

Hydraulic Cylinder Parts and Production

Double acting single shaft hydraulic cylinders are among the most produced hydraulic cylinders. For this reason, this type of cylinder will be examined as an example in this article.

The hydraulic cylinder will be produced from commonly used steel materials through machining and welding operations. Hard chrome coated Ck45 steel material is often preferred for shaft manufacturing. Cast iron or ductile iron steel can be used in the manufacturing of the front throat and piston. St52–3 steel material is often used in other parts.

In the production process, firstly, the raw material will be procured according to the part dimensions and will be cut with a saw according to the part dimensions. After cutting, the raw materials will be processed by machining operations on lathe and milling machines. Welding operations will also be carried out along with machining operations. Finally, the finished parts and sub-assemblies will be assembled using hand tools so that the hydraulic cylinder will take its final form. In the next subheading, the mentioned production steps will be detailed one by one, but before that, it will be explained which machines are used in the production process.

The production machines required to implement the production operations mentioned in the previous paragraph are mainly metal cutting saw, lathe, milling machine, circular welding machine and sleeve welding machine. The saw is used to cut metal raw material, usually purchased in long strips, into piece dimensions.

The lathe, another production machine, is used to process parts with axial symmetry. In the hydraulic cylinder that we will examine as an example, all parts except the joints have axial symmetry. For this reason, most cylinder parts are machined on a lathe. Moreover, in cylinder manufacturing, the lathe is expected to have a live tool feature. Live tools are used to create various asymmetric structures on the parts (for example, the hole on the barrel) and increase productivity by shortening production time. Another feature that should be present in a lathe is the lathe fixed bed. When processing parts such as barrels and shafts that are relatively longer than their diameter, it is necessary to support the part with a fixed bearing to prevent runout.

Unlike the lathe, only joints are machined on the milling machine. Moreover, if the lathe does not have a live tool feature, the milling machine can be used to create asymmetric structures on the parts.

Automatic welding machines are necessary to perform welding operations quickly and error-free. Circular welding machine; It is used to weld coaxial parts such as the back cover and the sleeve. On the other hand, the cot welding machine, as its name suggests, is used to weld cots to parts such as sleeves.

In this subheading, the cylinder whose production will be examined is introduced as an example and how it will be produced is briefly mentioned. Then, the production machines required for the production of this cylinder were mentioned. In the next section, the production process of the cylinder and the design of the parts will be discussed in detail.

Hydraulic Cylinder Production Operations Step by Step

As mentioned before, the production process; It starts with raw material supply and saw cutting, continues with machining and welded manufacturing operations, and finally ends with the assembly of sub-assemblies to each other. This long scheme will be examined in small sections in the following paragraphs. It should also be noted that the lubrication nipples, sleeves, bearings, piston rings, nuts and seals seen in the diagram; It is often purchased from external suppliers. For this reason, the production of the mentioned parts will not be discussed.

Saw cutting steps, which is the first step of the production process, can be seen. As mentioned before, metal raw material is mostly sold in the form of long bars or tubes. Therefore, the pipe or bar whose dimensions are ordered according to the part is cut according to the length of the part. Automatic band saw is mostly used for cutting. After the cutting process, the raw workpiece can now be connected to the lathe or milling machine and processed.

The first three operations of the workpiece that will become a sleeve are shown. Tubular part; The inner surface is supplied with H8 tolerance and honed. Since the piston seals will move in contact with the inner surface of the barrel, it is of great importance that the honed surface is scratch-free. As can be seen in the flow chart, in the first operation, the face surface of the workpiece is machined and the welding mouth is opened, the hydraulic oil hole is opened with the help of a live tool, and for a good bearing, the part of the outer surface that will sit on the bed is machined and its roughness and ovality are reduced. After this operation, the sleeve is welded onto the drilled hole using an automatic welding machine. Then, the workpiece is fastened to the lathe again, the other face surface is machined, and the inner surface is threaded. The reason why thread cutting is done after welding is that the welding process may cause deformation on the teeth.

The machining and welding operations to be performed on the workpieces that will become the back cover and the joint, and the subsequent assembly operations on the joint are shown respectively. The back cover is machined on the lathe, first with the back surface and then with the front surface, and a hole is opened for the hydraulic oil flow with the live tool. The joints are machined on the milling machine. The rear cover and joint, whose machining operations are completed, are then welded together. In order to weld the joint and the rear cover coaxially, a small pin on the rear cover and a pin hole of the same size in the joint have already been created. This pin and hole engage each other, ensuring that the parts are concentric during the welding operation. Finally, the bearing is driven into the joint, the piston ring is placed and the lubrication nipple is screwed into the joint. Hammering the bearing immediately after the welding process, while the parts are still hot, allows the bearing to pass easily into the expanded gap.

Welded manufacturing operations to be performed on the barrel and back cover are shown. The sleeve and back cover are welded using a circular welding machine. There is a small spot hole at the top of the joint to connect these two parts to the circular welding machine. While the front of the bucket is connected to the chuck, the rear cover is fixed with the tailstock hole at the top of the joint. After this operation, the sleeve part of the hydraulic cylinder is finished.

Machining operations of other parts at the beginning of the flow chart are shown. While the piston, front throat and shaft are machined on the lathe, the other joint of the cylinder is machined on the milling machine. The outer surface of the shaft has f7 tolerance and is hard chrome plated. It is of great importance that this coating, which is preferred for its corrosion resistance, surface hardness and low surface roughness, is not damaged or scratched. The reason for this is that the outer surface of the shaft, just like the inner surface of the barrel, will move in contact with the throat seals. After the machining of the shaft and joint is completed, the shaft is welded to the joint. The pin and hole used for centering the joint and the back cover are also applied to the shaft and joint. Just like the previous joint, the bearing is driven in after welding while the parts are hot. Finally, the piston ring is placed and the lubrication nipple is screwed on.

The assembly of the parts completed in the previous paragraph is shown in Picture 12. First, felts; It is placed in the channels on the piston and front throat. During this operation, it is important that the channels are clean, free of burrs and scratches, so that the seals operate without being damaged. Then, the surfaces that will come into contact with hydraulic oil are lubricated with system oil and the parts are assembled. The sub-assembly is completed by tightening the nut that will hold the last piston.

The two subassemblies, which are the final stage of manufacturing, are assembled with each other. First of all, the piston is placed in the sleeve. Then the front neck is screwed to the barrel with a toggle wrench. Holes in the outer diameter of the front throat are drilled so that this key can grip the front throat. With this operation, the production of the hydraulic cylinder is completed.

The finished cylinder is tested. If the tests pass successfully, the cylinder is packaged and prepared for shipment. The lifespan of a well-designed and regularly maintained cylinder can last for years.

The manufacturing of the hydraulic cylinder was examined from start to finish. All stages were presented using manufacturing methods common in hydraulic cylinder manufacturing. However, it should not be forgotten that there can be many different ways to manufacture a part. For example, joints can be manufactured as metal casting rather than machining. Moreover, the hydraulic cylinder examined in the article was specifically a double-acting, single-shaft hydraulic cylinder with a front neck screwed to the sleeve and a rear cover welded to the sleeve. However, since hydraulic cylinders can be of many different types and sizes, each design is unique and can naturally be produced with different methods. Examples of different types of cylinders: Rod type cylinders (tie-rod cylinders), telescopic cylinders, tandem cylinders, double shaft cylinders, ram type single acting cylinders can be given. Naturally, the manufacturing of the cylinder examined in this article is not valid for every cylinder.