With the development of the market economy, the mechanical manufacturing industry and the hardware industry have made rapid progress, attracting a large number of people from different industries to join. Therefore, many friends are at a loss when it comes to purchasing machine tools. Here are some basic purchasing knowledge for newcomers in the industry.
Consider the following factors:
1. Workpiece: The first important consideration is the parts you need to produce. The key point is to purchase a machine that can complete the processing tasks with the shortest workbench length and smallest tonnage. Carefully consider the material grade, maximum processing thickness, and length. If most of the work involves low carbon steel with a thickness of 16 gauge and a maximum length of 10 feet, a bending force of more than 50 tons is not necessary. However, if you are engaged in a large number of bottom-die forming, you may consider a machine with a tonnage of 150. Assuming the thickest material is 1/4 inch, a 10-foot free bending requires 165 tons, while bottom-die forming requires at least 600 tons. If most of the workpieces are 5 feet or shorter, the tonnage can be reduced by half, greatly reducing the cost of purchase.
2. Deflection: You also need to consider the deflection that may occur in the machine. Under the same load, the deflection of a 10-foot machine's workbench and slide is four times that of a 5-foot machine. This means that shorter machines require fewer shim adjustments to produce qualified parts, reducing preparation time. Material grade is also a key factor. Compared with low carbon steel, stainless steel usually requires about 50% more load, while most grades of soft aluminum reduce the load by about 50%. You can always get a tonnage table from the bending machine manufacturer, which shows the estimated tonnage required per foot length under different thicknesses and materials.
3. Bend radius of the parts: When using free bending, the bend radius is 0.156 times the opening distance of the bottom die. In the process of free bending, the opening distance of the bottom die should be 8 times the thickness of the metal material. If the bend radius is close to the material thickness, bottom-die forming is required. However, the pressure required for bottom-die forming is about 4 times larger than that of free bending. If the bend radius is smaller than the material thickness, a punch with a front-end radius smaller than the material thickness should be used, and the stamping bending method should be used to compensate for the springback and keep the material at around 90 degrees of excessive bending. Generally, the springback angle generated by the free bending mold on a new bending machine is ≤2°, and the bend radius is 0.156 times the opening distance of the bottom die. For bottom-die forming, the mold angle is generally 86-90°. There should be a gap slightly larger than the material thickness between the top and bottom dies at the end of the stroke. The forming angle can be improved because the tonnage of bottom-die forming is larger (about 4 times that of free bending), reducing the stress that usually causes springback within the range of bend radius. The stamping bending is the same as the bottom-die forming, except that the front end of the punch is machined to the required bend radius, and the gap between the top and bottom dies at the end of the stroke is smaller than the material thickness. Due to the application of sufficient pressure (about 10 times that of free bending), the front end of the punch is forced to contact the material, basically avoiding springback. In order to choose the lowest tonnage specification, it is best to consider a bend radius greater than the material thickness and use free bending as much as possible. When the bend radius is larger, it often does not affect the quality of the finished product and its future use.
4. Accuracy: Bending accuracy is a factor that needs to be carefully considered, which determines whether you need a CNC bending machine or a manual bending machine. If the bending accuracy requires ±1° and cannot be changed, you must consider a CNC machine. The repeat accuracy of the CNC bending machine slide is ±0.0004 inches, and the angle of forming must be within this accuracy with good molds. The repeat accuracy of the manual bending machine slide is ±0.002 inches, and under the conditions of using appropriate molds, it generally produces a deviation of ±2-3°. In addition, CNC bending machines are prepared for quick mold installation, which is an undeniable consideration when you need to bend many small batch parts.
5. Molds: Even if you have a full shelf of molds, don't assume that these molds are suitable for the newly purchased machine. You must check the wear of each mold by measuring the length from the front end of the punch to the table shoulder and the length between the table shoulders of the bottom die.
For standard molds, the deviation per foot should be around ±0.001 inches, and the total length deviation should not exceed ±0.005 inches. For precision ground molds, the accuracy per foot should be ±0.0004 inches, and the total accuracy should not exceed ±0.002 inches. It is best to use precision ground molds for CNC bending machines and standard molds for manual bending machines. Indeed, we often make the mistake of only buying new bending machines without purchasing suitable molds to match them.
6. Length of bent edges: One factor that is often overlooked is the length of the bent edges of the material before it enters the bending machine. Assuming a 90° bend is made along a 5x10 feet, 10-gauge low carbon steel plate, the bending machine may need to apply an additional 7.5 tons of pressure to lift the steel plate, and the operator must be prepared for the drop of a straight edge weighing 280 pounds. Manufacturing such parts may require several strong workers or even a crane. Bending machine operators often need to bend long side parts without realizing how much effort their work requires. Now there is a material support device suitable for workshops that handle this type of work, and this device can be improved according to the needs of new and old machines. With this device, forming long side parts only requires one person to operate.
Consider the following factors:
1. Workpiece: The first important consideration is the parts you need to produce. The key point is to purchase a machine that can complete the processing tasks with the shortest workbench length and smallest tonnage. Carefully consider the material grade, maximum processing thickness, and length. If most of the work involves low carbon steel with a thickness of 16 gauge and a maximum length of 10 feet, a bending force of more than 50 tons is not necessary. However, if you are engaged in a large number of bottom-die forming, you may consider a machine with a tonnage of 150. Assuming the thickest material is 1/4 inch, a 10-foot free bending requires 165 tons, while bottom-die forming requires at least 600 tons. If most of the workpieces are 5 feet or shorter, the tonnage can be reduced by half, greatly reducing the cost of purchase.
2. Deflection: You also need to consider the deflection that may occur in the machine. Under the same load, the deflection of a 10-foot machine's workbench and slide is four times that of a 5-foot machine. This means that shorter machines require fewer shim adjustments to produce qualified parts, reducing preparation time. Material grade is also a key factor. Compared with low carbon steel, stainless steel usually requires about 50% more load, while most grades of soft aluminum reduce the load by about 50%. You can always get a tonnage table from the bending machine manufacturer, which shows the estimated tonnage required per foot length under different thicknesses and materials.
3. Bend radius of the parts: When using free bending, the bend radius is 0.156 times the opening distance of the bottom die. In the process of free bending, the opening distance of the bottom die should be 8 times the thickness of the metal material. If the bend radius is close to the material thickness, bottom-die forming is required. However, the pressure required for bottom-die forming is about 4 times larger than that of free bending. If the bend radius is smaller than the material thickness, a punch with a front-end radius smaller than the material thickness should be used, and the stamping bending method should be used to compensate for the springback and keep the material at around 90 degrees of excessive bending. Generally, the springback angle generated by the free bending mold on a new bending machine is ≤2°, and the bend radius is 0.156 times the opening distance of the bottom die. For bottom-die forming, the mold angle is generally 86-90°. There should be a gap slightly larger than the material thickness between the top and bottom dies at the end of the stroke. The forming angle can be improved because the tonnage of bottom-die forming is larger (about 4 times that of free bending), reducing the stress that usually causes springback within the range of bend radius. The stamping bending is the same as the bottom-die forming, except that the front end of the punch is machined to the required bend radius, and the gap between the top and bottom dies at the end of the stroke is smaller than the material thickness. Due to the application of sufficient pressure (about 10 times that of free bending), the front end of the punch is forced to contact the material, basically avoiding springback. In order to choose the lowest tonnage specification, it is best to consider a bend radius greater than the material thickness and use free bending as much as possible. When the bend radius is larger, it often does not affect the quality of the finished product and its future use.
4. Accuracy: Bending accuracy is a factor that needs to be carefully considered, which determines whether you need a CNC bending machine or a manual bending machine. If the bending accuracy requires ±1° and cannot be changed, you must consider a CNC machine. The repeat accuracy of the CNC bending machine slide is ±0.0004 inches, and the angle of forming must be within this accuracy with good molds. The repeat accuracy of the manual bending machine slide is ±0.002 inches, and under the conditions of using appropriate molds, it generally produces a deviation of ±2-3°. In addition, CNC bending machines are prepared for quick mold installation, which is an undeniable consideration when you need to bend many small batch parts.
5. Molds: Even if you have a full shelf of molds, don't assume that these molds are suitable for the newly purchased machine. You must check the wear of each mold by measuring the length from the front end of the punch to the table shoulder and the length between the table shoulders of the bottom die.
For standard molds, the deviation per foot should be around ±0.001 inches, and the total length deviation should not exceed ±0.005 inches. For precision ground molds, the accuracy per foot should be ±0.0004 inches, and the total accuracy should not exceed ±0.002 inches. It is best to use precision ground molds for CNC bending machines and standard molds for manual bending machines. Indeed, we often make the mistake of only buying new bending machines without purchasing suitable molds to match them.
6. Length of bent edges: One factor that is often overlooked is the length of the bent edges of the material before it enters the bending machine. Assuming a 90° bend is made along a 5x10 feet, 10-gauge low carbon steel plate, the bending machine may need to apply an additional 7.5 tons of pressure to lift the steel plate, and the operator must be prepared for the drop of a straight edge weighing 280 pounds. Manufacturing such parts may require several strong workers or even a crane. Bending machine operators often need to bend long side parts without realizing how much effort their work requires. Now there is a material support device suitable for workshops that handle this type of work, and this device can be improved according to the needs of new and old machines. With this device, forming long side parts only requires one person to operate.
