Metal Powder and Wire Additive Manufacturing Technology

. Additive manufacturing techno logy can quick ly manufacture parts with dense microstructures and excellent mechanical properties, so that it shows a broad application prospect in aerospace and other fields. Additive manufacturing tec hnology w as briefly in troduced in th is paper. On th is basis, the technology and ch aracteristics of m etal powder and wire add itive manufacturing wer e systemati cally analyzed and compared, and the development of additive manufacturing technology was prospected.


Introduction
Additive manufactu ring also k nown as 3D p rinting, is a technology that combines subjects suc h as materials science and computer aided design. Through the control of the s oftware and the numerical c ontrol system, t he corresponding ra w mate rials are melted, sintered, a nd light-cured ac cording t o t he t hree-dimensional m odel, and physical o bjects are p roduced l ayer by l ayer. Compared with the p ast machining method s o f cutting and assemb ling raw materi als, it is a manufacturing method in wh ich materials are sup erimposed from bottom to t op [1,2] . Th is makes it po ssible to mak e complex structural parts that were pre viously restricted by trad itional production methods and were d ifficult to achieve [3,4] . With th e rap id development of th e manufacturing i ndustry i n the 21 st cent ury a nd t he proposal of "M ade in Ch ina 2025", ad ditive manufacturing technology has received wide attention. It has mad e great p rogress in military man ufacturing, medical i ndustry, automobile m anufacturing, construction industry, aeros pace, food indust ry, s mall jewelry manufacturing and other aspects [5] .
This article outlines the classification of additive manufacturing, and expou nds the research status of metal powder and wire additive manufacturing technology. In addition, the characteristics and applications of metal powder and wire additive manufacturing technolo gy are compared and analyzed.
This has certain theoretical and practical value for the realization of n ew materials and new technologies in the rapid manu facturing of p arts and in telligent manufacturing in the future.

Classification of additive manufacturing
Additive manufacturing started from the end of t he 90th century to the middle of the 20th century. It can be sai d that th e fo cus of add itive tech nology is lay ered manufacturing. The cl assification of co mmonly used additive manufacturing is shown in Table 1 [6,7]. The strip add itive manufactu ring techno logy is mainly used for the forming of lar ge p arts an d the welding r epair wo rk of surfacing welding. How ever, there are few app lications in ad ditive forming p arts, especially 3D prin ting, and th ere are relatively few response supp orting equ ipment. At present, metal powder an d wire a re th e main research d irections of additive manufacturing.

Metal powder additive manufacturing technology
Metal powd er add itive manufacturing mainly cov ers electron beam p owder add itive manu facturing, laser powder add itive man ufacturing, an d plasma powd er additive manufacturing.
According to th e mode of powder feed ing, t he powder add itive manu facturing tech nology is mai nly divided i nto t wo t ypes: powder s preading an d p owder feeding. In the technology of powd er spreading additive manufacturing, a layer of powder is laid on the table, and the co rresponding heat sou rce is co ntrolled by th e computer to selectively sintering the powder according to the predetermined path. Sintered ground is co nvenient to form th e solid part of t he parts, and finally the e xcess part can be remov ed fro m th e material to ob tain th e forming parts. A representative technique of this form is selective laser meltin g (SLM ) [8,9]. SLM sch ematic diagram is shown in Figure 1. It uses the heat of the laser beam to melt th e metal powd er, th en it fo rms p arts through c ooling an d s olidification p rocess. It has t he characteristics of no binder, high f orming p recision and good mecha nical properties. H owever, SL M t echnology is also limited by so me conditions, such as high requirements for material g ranularity, so it is d ifficult to make. It's n ot suita ble f or l arge parts an d the re pair o f failed parts.
In th e techno logy of powd er feeding add itive manufacturing, h eat sou rce an d pow der feeding nozzle are put together to make the powder directly sprayed into the mo lten pool. Th e t ypical tech nique in th is form is laser meltin g deposition (LM D) [10]. LM D techn ology does not require moulds and can be used to produce parts with co mplex shapes. However, th e h igh fo rming sp eed will reduce t he size accurac y. LMD has l ow production efficiency, but relatively high cost.
From th e ab ove analysis, it can be seen that metal powder add itive manu facturing tech nology is mai nly related t o t he quality requ irements of t he powder itself and the way of powder spreading or distribution, as well as the external heat sour ce. Gen erally speaking, th e forming quality of metal powd er additive is high, which is especially suitable for t he production of precision small p arts. Ho wever, it h as h igher requ irements on th e equipment an d e nvironment of p owder m anufacturing. The cost of powder manufacturing is higher than that of silk, but the efficiency is lower.

Metal Wire additive manufacturing technology
In add itive man ufacturing of metal wire, the metal wire is easy to mak e and ch eap. In particular, th e add itive manufacturing technology with wire as electrode has obvious advantages in wel ding spee d. It does not need additional wire feed ing equ ipment, so it can save sp ace and increase efficiency.

Laser fuse additive manufacturing technology
Laser fu se additiv e man ufacturing techno logy is t o melt and accumulate the wire fe d into the laser beam throug h the laser heat to form the required parts. It is often called laser co ld wire add itive man ufacturing tech nology. Th e diameter of the laser fuse is small and t he appearance of parts is good.

Non-consumable electrode metal wire additive manufacturing technology
The non-consumable electro de metal wire add itive manufacturing tech nology is a k ind o f ad ditive technology which uses t he corre sponding plasma, electrode beam and tungsten electrode arc as heat source to melt the wire b eing sent in and th en form it. Tun gsten inert gas wel ding (TIG) ad ditive manu facturing is a typical metal ad ditive manufacturing tech nology in which wire i s not use d as el ectrode. It has t he characteristics of good fo rming qu ality and fo rming efficiency [1 1]. It is a kind of ad ditive man ufacturing technology th at p eople are ex ploring gradually, or will become the mainstream in the future.

Consuming electrode metal wire additive manufacturing technology
The con suming electrode metal wire add itive manufacturing tech nology is main ly th e meth od of melting a nd stacking met al wi re b y using t he a rc generated between the wire and the workpiece as the heat source. Cold metal transition weld ing (C MT) additive manufacturing technology has wi dely used in recent years. Generally this kind of additive technology has fast forming sp eed and high pr oduction eff iciency, but th e surface is rough. CMT has the characteristics of low heat input an d no sp lash, which has attracted wi de atten tion [12].

Conclusion and Prospect
Through th e sy stematic an alysis of metal p owder an d metal wire ad ditive man ufacturing tech nology, it is concluded that metal p owder additive manufacturing has high co st and go od forming quality, bu t lo w forming efficiency. The add itive manufacturing tech nology of fused el ectrode met al wi re has high f orming e fficiency and l ow co st. Its app earance forming quality is wo rse than t hat of powder ad ditive. It needs to be processed again. Th e fo rmability and manufacturing co st of additive man ufacturing techn ology of non-fused metal wire are between the above two.
Additive manu facturing tech nology is a mu ltidisciplinary tech nology with many influ encing factors. Therefore, it is no t limited t o study one su bject, but to increase th e cro ss-integration research of add itive manufacturing researchers in multiple subjects and fields. At present, there is still a lack of a comp lete set of standards fo r ad ditive manufacturing techno logy and its quality ev aluation. Th e relevant departments sho uld speed up th e formu lation o f techn ical an d quality standards for additive manufacturing industry.