Wire-cut machine tools are precision machining equipment, and relevant national departments have formulated a series of technical standards for their production, manufacture, and accuracy testing. However, due to high market demand, some manufacturers ignore quality in order to increase output. In particular, some private small enterprises in eastern China that do not possess the conditions for machine tool production are also manufacturing wire-cut machine tools, substituting inferior products for good ones, causing inconvenience to many users, especially foreign users, when selecting models. A slight misstep can result in user's own interests being harmed, so it is particularly important to determine the manufacturer and brand during selection.
Firstly, one should determine the functions and specifications of the machine tool based on their own products and production needs. When selecting a model, users often overlook future development requirements because machine tools are not consumables. Although the initial investment is large, their service life is long. If one only considers the present and does not take into account the company's own development factors, there will inevitably be repetitive investments in the near future. We have encountered many such cases with shearing machines. Therefore, when selecting a model, one should have a forward-looking awareness and developmental perspective, meaning that the selected machine tool should have reserves both in function and technology level.
Secondly, it is about how to determine the manufacturer, focusing on comparisons of quality, reputation, and product prices. Regarding quality and reputation, consider the following aspects:
(1) Production scale: too small a scale makes it easy to be eliminated in fierce market competition, and lacks strength in product research and innovation.
(2) Production method: whole machine manufacturers can effectively control the quality of each production process, while assembly-style production has no control over the intrinsic quality of the machine tool or the entire production process. This is because the main components of such machine tools are CNC system productions completed by other manufacturers. Currently, developed countries more commonly adopt this socialized production method for complex products, which premise on a complete market system and sound commercial law. In this aspect, China still has a gap, so we remind users to pay sufficient attention to the production method of the manufacturer.
The third aspect is price, which is the most sensitive issue for both users and manufacturers. However, one point is consistent: product performance is the basis of price, and product price reflects performance and quality, what we often call performance-to-price ratio. Therefore, discussing price without considering performance is meaningless. High prices may not be acceptable to users, just as low prices are not necessarily good either, as low prices mean manufacturers must cut costs (businesses cannot operate at a loss), but quality and cost have a critical point. Below this point lies purely inferior products, like some wire-cut machine tool manufacturers in eastern China. Therefore, users should remember that wire-cut machine tools are precision processing equipment used for a long time when considering price.
The fourth aspect is "hearsay is false, seeing is believing." Due to intense market competition, manufacturers may reveal some intentional disparaging words or actions against each other. Although this mentality can be understood, it disrupts the selection environment for users. Thus, these manufacturers' inappropriate behaviors themselves show irresponsibility to users. However, if users focus on reality, these interferences become invalid. Therefore, when purchasing wire-cut machine tools, users must see physical objects and samples, especially high-thickness demonstrations, so they can make informed decisions.
In selecting wire-cut machine tools, users should correctly recognize the relationship between quality and service:
The ultimate purpose of both product quality and after-sales service is to ensure users' normal use of the product. Zero fault rate is an enterprise's eternal pursuit goal. Excellent quality is the foundation of after-sales service, and after-sales service is the continuation of product quality. We believe that high-quality products must come from capable regular enterprises, and such enterprises also value after-sales service to guarantee their own credibility. Additionally, good product quality leads to fewer faults, thus reducing after-sales service costs. Although both are indispensable, users should primarily focus on product quality. No matter how good the after-sales service is, it can only be a way to compensate for quality issues. A mature and reliable wire-cut machine tool already considers reducing fault rates and making maintenance services more convenient during its design and development. The quality of after-sales service first reflects a company's values and moral level, secondly its management ability and the virtues of service personnel. Only those companies with strength and development potential, who view brands as life, can possess these three aspects.
When selecting a model, how to judge the accuracy retention of the machine tool:
In mold processing, wire-cut processing is generally the final procedure, so the requirement for processing accuracy is very high. If the mechanical accuracy of the machine tool is poor, it will directly affect the processing quality of products and molds, ultimately leading to losing users and markets. Therefore, when selecting a wire-cut machine tool, judging the mechanical accuracy and structure's merits and demerits is very important.
Generally speaking, it is easier to judge the accuracy of new machine tools because there are national standards such as GB7926m87 and related machine tool accuracy universal standards. During the adjustment and acceptance of new machine tools, it can be determined whether they are qualified or not. However, the most important thing is to judge the accuracy retention of the machine tool because the good or bad of machine tool accuracy retention only becomes apparent after a certain period of use, and national standards cannot strictly quantitatively control it. Therefore, users must thoroughly understand the machine tool and its structure during selection, avoiding hearsay and unfounded rumors, which could disturb your judgment.
Below, we will elaborate from several aspects such as the transmission structure of the machine tool worktable, guide rail structure, and drive mode.
4-1. Ball screw and its installation structure
Although the accuracy of the ball screw is important, if its installation structure is unreasonable, even the best ball screw is useless.
First, observe the form of the ball screw, whether it is a ball screw, triangular thread screw, or trapezoidal thread screw. On wire-cut machine tools, ball screws are superior to triangular thread screws and trapezoidal thread screws, and the diameter of the ball screw should be as large as possible to increase rigidity.
Second, the installation structure of the ball screw, as it belongs to precision transmission components, to fully utilize its precision, higher requirements are placed on its assembly structure. It must be fixed at both ends with bearing support. For large stroke machine tools, pre-stretching the ball screw is necessary to reduce its deflection, thereby improving the motion accuracy of the machine tool worktable.
4-2. Gear transmission structure
(1) First, you need to fully understand the number of gears inside the gearbox. The more gears participating in the transmission, the greater the transmission resistance, the easier the gear surface wears out, the easier the transmission produces gear clearance, leading to a larger systematic error in the machine tool worktable. The more gears, the easier occasional errors occur if assembled poorly, so fewer transmission gears are better. Adopting a pair of gears results in the smallest transmission error, so understanding the gear transmission structure of the worktable movement is crucial when selecting a model.
(2) Carefully observe the working environment and lubrication performance of the worktable transmission gearbox. Some manufacturers' early machine tools, due to unreasonable design, allow cutting fluid to easily enter the gearbox, causing gears to work submerged in cutting fluid for a long time, which is very unreasonable. At minimum, it increases gear wear, and at worst, causes step motors to get waterlogged and burn out. Therefore, users must observe the position of the worktable gearbox during selection to ensure cutting fluid does not infiltrate, which is crucial for the accuracy retention of the machine tool.
4-3. Guide rail rigidity and overall structure
(1) The guide rail is the key to ensuring the motion accuracy of the worktable, and users should pay high attention during selection. First, observe the size of the cross-section of the guide rail. Under the same conditions, the thicker the guide rail, the better the rigidity, and the less likely it is to deform during processing. Secondly, inquire about the material and heat treatment process of the guide rail from the manufacturer. Generally speaking, to ensure its strength and minimize deformation, high-carbon alloy steel, integral quenching, or medium-frequency quenching processes are preferable.
(2) Directly observe the guide rail structure. Common guide rail structures on the market include:
1 Embedded steel ball type rolling guide rail;
2 Embedded steel roller type rolling guide rail;
3 Linear rolling guide rail;
4 Elastic bearing cast iron guide rail.
The difference between the first and second types lies in the rolling elements of the guide rail, one being balls and the other rollers. Balls contact the guide rail surface at points, while rollers contact the guide rail surface along lines, so its wear resistance and load-carrying capacity are much better than ball types. Elastic bearing cast iron guide rails are a simple type that has been phased out. Currently, imported machine tools from Japanese Sodick Company, Japanese Mitsubishi Company, Swiss Charmilles Company, and Swiss Riaqi Company all adopt the second and third types of structures. Therefore, through comparison, users should consider the second and third types of structures during selection.
4-4. Drive method
Numerical control wire-cut machine tools are generally driven by stepper motors, which can be further divided into reactive and hybrid types to achieve different step angles. The most common type on the market is the reactive stepper motor, which has different driving methods such as three-phase three-step, three-phase six-step, five-phase ten-step, and five-phase double ten-step. This type of motor has a large step angle and only three-phase windings. With continuously increasing market demands and the improvement of overall requirements by relevant departments of the National Machinery Industry Ministry for the machine tool industry, five-phase ten-step will gradually replace three-phase six-step. This is because five-phase ten-step not only subdivides the step angle of three-phase six-step further but also increases the motor winding to five phases, so the transmission is smooth and powerful.
To summarize, in order to ensure the long-term reliability of the machine tool accuracy, users should select the following structure during selection:
(1) Choose precision ball screws with as large a diameter as possible, and ensure both ends have fixed bearing support structures.
(2) The transmission gears of the worktable should be minimal, preferably just one pair of gears, and the position and structure of the gearbox must ensure that it absolutely cannot immerse in cutting fluid.
(3) Preferably choose rolling guides with a large cross-sectional area or a high width-to-thickness ratio or linear guides.
(4) Select the five-phase ten-step stepper motor drive method; if conditions permit, choose the hybrid subdivision drive or AC servo drive for better results.
5. What issues should be noted when purchasing large-scale wire-cut machine tools?
Large-scale wire-cut machine tools, due to their large processing range and strong load-bearing capacity (such as DKM800 type from Shenyang Machine Tool Co., Ltd., X and Y travel is 800t1000, carrying capacity reaches over 2000Kg), are incomparable with foreign machine tools when processing large molds, so the benefits they can create are very considerable. However, if problems arise with the machine tool, especially if there are inherent quality issues within the machine tool itself, the losses caused can also be severe. Therefore, selecting large-scale wire-cut machine tools must be done with particular caution.
Due to their large stroke and large load-bearing characteristics, the selection should focus on the structure and rigidity of the machine tool to ensure reliable accuracy during the processing of large workpieces. There are obvious differences in structure compared to small and medium-sized wire-cut machine tools:
1. The worktable must adopt a full-support structure to improve the rigidity of the machine tool and ensure heavy loads without deformation.
2. Use imported linear guides to ensure good sensitivity and motion accuracy under heavy loads.
3. Compared to small machine tools, the diameter of the ball screw must be increased.
4. If the user has a certain strength, the worktable of the machine tool is preferably driven by an AC servo motor, whose features include accurate precision, fast movement speed, high reliability, and convenient operation.