How to punch press w orcs ?
The design of a punching machine is based on the principle of converting circular motion into linear motion. The flywheel is driven by the main engine, while the gears, crankshaft or eccentric gear, and connecting rod are driven by the clutch to produce the linear movement of the slider.
The movement from the prime mover to the connecting rod is circular, so there must be a transfer point between the connecting rod and the slider to accommodate both circular and linear motion.
There are two main types of mechanisms in punch press design: ball type and pin type (cylindrical type). These mechanisms convert the circular motion into a linear motion of the slider.
During punching, the press applies pressure to the material, causing it to plastically deform. To obtain the desired shape and precision, a set of molds (upper and lower molds) must be used. The material is placed between the molds and deformed by the pressure of the punching machine.
The force exerted on the material during processing generates a reaction force, which is absorbed by the mechanical body of the punching machine.
Punch Press Classification
1. Classified by slider driving force
The driving force behind the slider can be mechanical or hydraulic, resulting in two different types of punch presses:
(1) Mechanical punching machine (mechanical press)
The use of a screw mechanism in the slide drive mechanism is known as a screw press.
(6) Rack press
(2) H frame punching machine
Currently, most punch presses used in the general stamping industry are C-frame presses, especially for smaller machines (below 150 tons). For larger machines, most of them are straight side presses (H frame).
Punch presses that use a C-frame body are called C-frame presses, while those that use a straight frame body are called straight side presses or H-frame presses.
(1) C-frame press
The asymmetrical body of a C-type punching machine leads to deformation of the front and rear openings of the body during punching, which affects the parallelism of the tooling. This is the main disadvantage of C-frame presses.
As a result, C-frame presses are typically used at only about 50% of their rated capacity. Despite this limitation, C-frame presses remain popular due to their excellent operability, easy mold access, and convenient mold changing process.
Additionally, the cost of a C-frame press is relatively low, making it the dominant type of press. However, its capacity is limited to 300 tons or less.
(2) Straight side press
Due to its symmetrical body, the straight side press is capable of handling eccentric loads during operation, but has limited access to the die during operation. This type of press is generally used for large machines, with a capacity exceeding 300 tons, and has an integrated body and three-stage construction.
Unhappy press selection
When selecting a punch press, it is crucial to have a clear understanding of its intended use. This requires a comprehensive understanding of processing methods, working methods, press functions and technological trends, as well as a solid understanding of market trends and situations.
However, the complexity of the processing method and press function often makes complete understanding difficult, leading to selections that are not based on a complete understanding of the intended use.
Particular care must be taken when choosing a punching machine for streamlining, as even a small error can have significant consequences. Choosing the wrong printer can result in reduced efficiency and wasted investment in equipment.
The punching capacity of a punching machine has three main components: pressure capacity, torque capacity and working capacity.
- Pressure capacity refers to the position of the slider at bottom dead center that is capable of generating a certain amount of pressure, also known as “nominal pressure” or simply “capacity”. This is expressed in tonnes.
- Torque capacity refers to the position where pressure capacity is generated, also known as the capacity generation point. It is expressed in mm.
- Work capacity is the maximum effective capacity, expressed in kg-m, that can be produced in a single stroke.
How to choose the right punch press
Correctly determine processing methods and working methods
(1) Correct Determination of Processing and Engineering Methods
There are several stamping methods and sometimes combined with machining. When choosing a press, it is important to assess whether the desired processing method is suitable for the target product and whether it is the ideal number of processing operations. The type of press to be selected is largely determined by the chosen processing method.
(2) Production Volume
For runs exceeding 3,000 to 5,000 pieces, it is advisable to use automatic feeding. When the production volume is high due to multiple processes, continuous processing and transfer processing should be considered, including high-speed automatic punching and transfer processing. Additionally, it is necessary to consider the use of automatic machines such as high-speed automatic presses and transfer presses.
The choice between universal or automatic press depends on the production volume, but the required quantity must be considered when necessary. It is important to maintain adequate inventory levels, taking into account not only current but also future production levels, market conditions and technological trends.
(3) Relationship between Shape, Quality and Size of Materials
The processing method, harvest yield and material utilization rate determine the shape and quality of the material. The shape of the material depends on whether it is a roll, a fixed-size material or a semi-processed product, and the size of the material, which affects the operation method.
(4) Material Handling: Supply, Production and Waste Management
The movement of materials covers the operations of supplying materials, removing products and disposing of waste. In production plants, material handling makes up a significant portion of overall operations. As a result, material movement should not be considered just a part of production, but should be evaluated in terms of the rationalization of the entire factory. The functions required in a press vary depending on material handling considerations.
(5) Using the matrix pad
For single-action presses in drawing operations, additional die pads should be considered. The die pad offers high performance, making it possible to perform complex drawing operations without using a double-action punch press. To improve the performance of the die pad, a locking device is required as an auxiliary device.
Select the suitable punching machine capacity for processing.
(1) Determine the machining pressure and pressure stroke curve
Calculate the maximum pressure required for machining and the pressure variation during the machining cycle.
For multiprocessing, it is important to calculate the pressure stroke curve for each process and then combine them to obtain the composite pressure stroke curve.
Establish the maximum pressure required for processing and the pressure stroke curve to select the appropriate pressure capacity.
Work capacity selection should be based on processing frequency (number of cycles per minute).
Punching machines equipped with an automatic feeding device should ideally have an engine with an increased power of one horsepower.
It is advisable to select a press capacity that is not just above your maximum limit for continuous use, but rather a more common capacity of 75-80% of rated capacity.
(2) Eccentric Loading and Concentrated Loading
Eccentric loading is commonly present in stamping processes, including those involving multiple dies or a continuous punching die on a single punch press.
It is important to keep in mind that punching capacity design is usually based on a central load and therefore the pressing capacity may be reduced if there is an eccentric load. To compensate for this, select a punching capacity with sufficient margin for eccentric load work.
Many cold forging processes involve extremely concentrated fillers. For this type of work, it is advisable to choose a press with the smallest possible space for the die.
(3) Reduction in effective die pad capacity
When a die pad is installed, the extension capacity of the press is equal to its capacity minus the pad. Pad capacity is typically 1/6 of the printer's rated capacity.
Although it may seem small, it is a significant value when compared to the effective near-center drawing capacity of a punch press. However, care must be taken when a high damping capacity (one third of the press capacity) is required for processing. This can significantly reduce the effective extension capacity near the midpoint of travel and, in extreme cases, the ability to push the pad may be lost.
Therefore, for such a high damping capacity, the torque capacity of the press must also be selected as high. If the damping capacity is too high, the structure may become uneconomical due to incompatible torque capacity, so a double-action press should be considered if necessary.
Clarify the dimensional accuracy of processed products
The precision of the processed product is determined by its intended use and its impact on subsequent processes.
There are numerous factors that can result in low machining precision, such as variations in the thickness of the material to be processed, the volume of the raw material block (in the case of extrusion processes), the properties of the material in relation to its resistance to deformation , the level of lubrication used and die wear, among others, depending on the specific production process.
If a high level of processing precision is required, it is recommended to choose a press with high rigidity or a press with a large capacity that can provide sufficient pressure for processing needs.
However, it should be noted that C-frame presses may not be as effective even with large capacity presses, and it is important to carefully select a press with high rigidity to obtain optimal results.
Fully understand the function of the punch press
(1) Complete evaluation of press specifications
Printer specifications provide information about the printer's main capacity and size and are crucial in determining the right printer for your needs.
It is important to note that the press capacity indication typically reflects pressure capacity only, and a comprehensive assessment should include both torque capacity and working capacity.
When using the press for blasting, it is recommended to choose one with a shorter stroke and higher SPM.
Various factors such as the height of the die, the width of the work surface, the T-slot for mounting the die, and the pin hole for the buffer must be considered in relation to the die to be used.
Keep in mind that pushing printer specifications to the limit due to factory constraints can negatively impact printer performance.
Therefore, it is recommended to choose a punching machine with standard specifications that has a proven track record and reliable operating history.
(2) Choice of press attachments
It is also important to carefully evaluate press accessories, as their proper use can significantly increase productivity.
To maximize production, consider installing an automatic feeder for continuous processing.
If continuous processing is challenging due to the complexity of material sourcing and product extraction, using a timer can help improve productivity.
The incorporation of conveyors or UNLOADER units can also contribute to increased productivity.
For example, if the die needs to be changed frequently, a quick change device (QDC) for the die and its holder may be useful.
Consider accessories such as slow-running devices, material exchange systems, and product stacking devices.
Roller feed punching machines must be equipped with a variable speed device.
It is also important to prepare for the potential future need to install dampers, feeders or rotating cams.
However, having too many complex accessories can increase the failure rate and maintenance issues, so it is crucial to choose the appropriate accessories for your printer.
(3) Check the flexibility of the function
To maintain optimal yield, the press function must be in sync with the market trend of replacing old machines with new ones. This requires examining functions that can accommodate high and low production volumes and those that can be updated with future models.
For example, automatic feeder driving force is often derived from the punch crankshaft for perfect synchronization. However, if a stand-alone feeder is used, it offers additional flexibility as it can be easily relocated due to its independent power source, can be paired with any press, and can adapt to changing working conditions.
(4) Select a reliable and easy-to-maintain punching machine
Stamping products are often produced in large quantities and involve multiple processes, so any breakdown in a pressing machine can have a significant impact on overall production. It is essential to choose a press that is easy to maintain, inspect and has a high degree of reliability, especially with regard to the stability and durability of the clutch, brake and electrical system.
(5) Ensure security measures are in place
Punching work can be highly dangerous, so it is important to consider safety measures and equipment when selecting a punch press. The press must be equipped with interlocking devices, shear plate and hydraulic overload safety devices, and safety devices for two-hand operation, linear and mechanical operations to ensure safe operation even in the event of malfunction.
(6) Consider noise and vibration limits
Noise and vibration levels in stamping plants are regulated by law for public health reasons. The operating environment is a crucial factor to consider, so it is necessary to check whether there are noise and vibration countermeasures in the pressing equipment.
(7) Automation is key
With the change in production pattern, batch size decreased, resulting in an increase in the frequency of mold and material changes. Automation is essential to save labor and time and to speed up the automatic stamping and processing line, including the selection and configuration of dies and materials, adjustment of punching machines, production operation and production volume management. With advances in technology, it is now possible for an unmanned press line to produce the desired product with precision, controlled by remote instructions.
