The ball screw is composed of a screw, a nut, a ball and a ball returning device, and its main function is to convert rotary motion into linear motion. It is widely used in precision equipment, especially in numerical control equipment. The pulse signal sent by the control system controls the rotation of the servo motor, and then the precision ball screw converts the rotation motion of the servo motor into the linear motion of the workbench, so as to realize the machining trajectory control of the workpiece. Therefore, the assembly process and precision detection are very strict, and the technical requirements for assembly workers are also high.

一、故障現象

1、 Fault phenomenon

某數控設備有限公司在數控車床精密滾珠絲杠裝配后進行靜態精度檢查時合格,但在試車后或使用一段時間后出現精密滾珠絲杠的軸向跳動嚴重超差,影響了機床的加工精度,設備返修率為43%,給企業帶來巨大的經濟損失和聲譽損失。

A numerical control equipment Co., Ltd. passed the static accuracy inspection after the assembly of the precision ball screw of the numerical control lathe. However, the axial runout of the precision ball screw was seriously out of tolerance after the test run or after a period of use, which affected the machining accuracy of the machine tool. The equipment repair rate was 43%, bringing huge economic losses and reputation losses to the enterprise.

二、故障原因分析

2、 Fault cause analysis

1.精密滾珠絲杠精度達不到要求

1. The precision of precision ball screw cannot meet the requirements

滾珠絲杠在入庫時已進行了精度檢驗,可排除本身的質量問題。但細長軸類零件(機床絲桿等)在保管時應該采用垂直放置,以免受重力變形影響精度。該滾珠絲杠采專用包裝箱垂直放置,在裝配后的靜態檢查合格,因此可以排除此項。

The ball screw has been inspected for accuracy when it is put into storage, which can eliminate its own quality problems. However, the slender shaft parts (machine tool screw rods, etc.) should be placed vertically during storage to avoid the influence of gravity deformation on the accuracy. The ball screw is vertically placed in a special packing box. After assembly, the static inspection is qualified, so this item can be excluded.

2.裝配不當損壞了絲杠的精度

2. Improper assembly damages the accuracy of the lead screw

通過了解,裝配工人對精密滾珠絲杠組件熟悉的,裝配時也是格外小心,完全按裝配工藝進行的,因此也排除了這種可能。

Through understanding, the assembly workers are familiar with the precision ball screw components, and they are also very careful when assembling. They are completely carried out according to the assembly process, so this possibility is also excluded.

3.機床行程超程,工作臺發生碰撞,導致精度損壞

3. The travel of the machine tool is out of range, and the workbench collides, resulting in accuracy damage

操作機床時發生超程,容易導致機床碰撞而引起的。但經了解機床的行程限位開關沒有問題,用戶也沒有這方面的意見反饋。

Overtravel occurs when operating the machine tool, which is easily caused by collision of the machine tool. However, it is understood that there is no problem with the travel limit switch of the machine tool, and the user has no feedback on this aspect.

4.檢測方法不正確,導致精度超差

4. The detection method is incorrect, resulting in out of tolerance of accuracy

檢驗員采用千分表配合磁力表座,以工作臺直線導軌滑座為檢測基準進行檢測,檢測方法及檢測基準也符合要求。

The inspector uses a dial indicator to cooperate with the magnetic meter base, and uses the linear guide rail slide of the workbench as the detection benchmark. The detection method and the detection benchmark also meet the requirements.

5.裝配工藝不正確,造成裝配誤差

5. Incorrect assembly process, resulting in assembly error

原裝配步驟是:先裝好直線導軌,以直線導軌的滑座為基準校正絲杠,再以絲杠兩端支承座安裝孔配作固定螺紋孔。用螺釘固定絲杠后,用磁力表座將千分表固定在直線導軌滑座上,測量絲杠、側母線和絲杠徑向跳動量,保證絲杠的平行度及跳動量在要求范圍內。重新配作支承座定位錐銷,裝好錐銷后再復檢一次。裝配各步驟采用的處理方法基本正確,檢測基準與工藝基準也相符,檢測量具精度也能滿足要求,被測要素也正確。整個裝配過程沒有問題,但通過在現場觀察,發現裝配工藝中仍存在以下問題:

The original matching steps are as follows: first install the linear guide rail, calibrate the lead screw based on the sliding seat of the linear guide rail, and then use the mounting holes of the bearing seats at both ends of the lead screw as fixed screw holes. After fixing the lead screw with screws, fix the dial indicator on the slide seat of the linear guide rail with the magnetic gauge base, measure the radial runout of the lead screw, the side bus bar and the lead screw, and ensure that the parallelism and runout of the lead screw are within the required range. Refit the positioning cone pin of the support seat, and recheck it after installing the cone pin. The processing methods adopted in each step of assembly are basically correct, and the test datum is consistent with the process datum. The accuracy of the measuring tools can meet the requirements, and the measured elements are also correct. There are no problems in the whole assembly process, but through on-site observation, it is found that the following problems still exist in the assembly process:

(1)使用手電鉆鉸孔時,由于鉸削余量較大,振動較厲害,雙手控制不穩,鉸刀擺動過大,造成錐孔鉸削后上大下小,錐度不是要求的1∶50。用涂色法進行檢查,發現錐銷與錐孔的接觸部位不正確,位置靠近小頭一端,不能保證良好的接觸精度,受到交變應力與振動時容易松動,從而導致定位精度下降。

(1) When reaming with hand electric drill, the reaming allowance is large, the vibration is severe, the control of both hands is unstable, and the reamer swings too much, resulting in the reaming of the tapered hole being large up and small down, and the taper is not required to be 1:50. It is found that the contact part between the taper pin and the taper hole is incorrect, and the position is close to the end of the small head, which can not guarantee good contact accuracy. It is easy to loosen when subjected to alternating stress and vibration, resulting in a decrease in positioning accuracy.

(2)機鉸后沒有留精鉸余量,也沒有進行手工精鉸。圓錐銷的配合都是依靠配合面的過盈產生摩擦力來定位的。由于機鉸后表面粗糙使實際過盈量減少,造成摩擦力不夠,自鎖性能下降,當受到交變應力與振動時容易松脫,從而導致定位精度下降。

(2) There is no allowance for fine hinge after mechanical hinge and no manual fine hinge. The fitting of conical pin is located by the friction force generated by the interference of the fitting surface. Due to the rough surface after the mechanical hinge, the actual interference amount is reduced, resulting in insufficient friction, and the self-locking performance is reduced. When it is subjected to alternating stress and vibration, it is easy to loose, resulting in the reduction of positioning accuracy.

(3)鉸孔時孔徑控制不嚴,鉸削過程中沒用錐銷試配,裝配時用銅棒輕輕敲入即可。由于不能保證足夠的過盈量,裝配后的摩擦力過小;受負荷及振動時易造成錐銷松動,失去定位作用,導致工作臺運動精度差。

(3) The hole diameter is not strictly controlled during reaming. During reaming, no taper pin is used for trial fitting. During assembly, a copper rod can be used to gently knock in. The friction force after assembly is too small due to insufficient interference; Under load and vibration, it is easy to cause the taper pin to loosen and lose the positioning function, resulting in poor movement accuracy of the workbench.

(4)在鉆孔鉸孔等過程中,沒有進行防塵處理。雖然絲杠副帶有防塵圈,但鑄鐵粉塵非常細小,且極易粘附在絲杠表面。如有少量進入絲杠副傳動面,粉塵的研磨作用會加劇絲杠副的磨損,導致絲杠精度下降,降低使用壽命。

(4) In the process of drilling and reaming, no dust-proof treatment was carried out. Although the lead screw pair is provided with a dust ring, the cast iron dust is very small and easily adheres to the surface of the lead screw. If a small amount of dust enters the transmission surface of the lead screw pair, the grinding effect of dust will aggravate the wear of the lead screw pair, resulting in the reduction of the accuracy of the lead screw and the reduction of the service life.

三、故障處理辦法

3、 Troubleshooting

1.使用機鉸粗鉸后必須留出精鉸余量,再手工精鉸

1. After the mechanical hinge is used, the fine hinge allowance must be reserved before manual fine hinge

這個方法可以糾正機鉸后的錐度誤差,降低孔壁的表面粗糙度值,提高配合面的接觸精度,保證足夠的摩擦力矩。

This method can correct the taper error after reaming, reduce the surface roughness of the hole wall, improve the contact accuracy of the mating surface, and ensure sufficient friction torque.

2.在鉸孔時應及時用錐銷試配

2. During reaming, taper pins shall be used for trial fitting in time

目的是方便控制鉸孔孔徑。當錐銷能用手插入銷長的80%～85%左右時孔徑才為合格;清理鐵屑后,應在錐銷上涂機油后再用銅棒打入與工件表面平齊,以保證足夠的摩擦力矩,防止在使用中受載荷而松動。

The purpose is to conveniently control the reaming hole diameter. The hole diameter is qualified when the taper pin can be manually inserted into about 80% ~ 85% of the pin length; After the iron scraps are cleaned, the taper pin shall be coated with oil and then driven with a copper rod until it is flush with the surface of the workpiece, so as to ensure sufficient friction torque and prevent loosening due to load during use.

3.做好絲杠表面的防塵處理

3. Conduct dust-proof treatment on the surface of the lead screw

在鉆孔、鉸孔及攻螺紋過程中,應作好絲杠表面的防塵處理。用清潔的布包裹住絲杠的外露部分,防止粉塵進入絲杠副傳動面,以延長精密元件的使用壽命,提高裝配精度。

In the process of drilling, reaming and tapping, the dust-proof treatment of the surface of the lead screw shall be done well. Wrap the exposed part of the lead screw with clean cloth to prevent dust from entering the drive surface of the lead screw pair, so as to extend the service life of the precision components and improve the assembly accuracy.

在制造汽車、手機、電腦等的機床及工業機器人、液晶顯示屏及半導體生產設備、生產塑料零部件的注塑機等領域，滾珠絲杠作為產品制造廠設備中的核心零件，發揮這重要作用。

In the fields of machine tools and industrial robots for manufacturing automobiles, mobile phones, computers, etc., liquid crystal displays and semiconductor production equipment, and injection molding machines for producing plastic parts, ball screws play an important role as the core parts in the equipment of product manufacturers.

正確的安裝絲杠能有效地提升設備的運轉精度、延長使用壽命。

The correct installation of the lead screw can effectively improve the operation accuracy and prolong the service life of the equipment.

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