yildiz technical university

ICAME2016 2ND INTERNATIONAL CONFERENCE ON ADVANCES IN MECHANICAL ENGINEERING

PROCEEDINGS BOOK

ORHAN ÇAKIR “CHEMICAL MACHINING OF CZ128 COPPER ALLOY”

pp:542-547 10-13 MAY, 2016

YILDIZ TECHNICAL UNIVERSITY

ISTANBUL, TURKEY 1

CONFERENCE ON ADVANCES IN MECHANICAL ENGINEERING ISTANBUL 2016 – ICAME2016 11-13 May 2016, Yildiz Technical University, Istanbul, Turkey

CHEMICAL MACHINING OF CZ128 COPPER ALLOY *Orhan Çakır Yildiz Technical University Besiktas, Istanbul, Turkey Keywords: Chemical machining, copper alloy, chemical etchant, depth of etch, surface roughness * Corresponding author, Phone: +90 212 3832750, Fax: +90 212 3833024 E-mail address: [email protected]

ABSTRACT Chemical machining method is applied to shape material under controlled corrosion environment. It is extensively used in production of complex parts from thin materials. It is also convenient in micromachining application. Copper and its alloys are vital engineering materials that are extensively used particularly in electronics industry due to their electrical properties. Chemical machining of copper and copper-based alloys are important due to these materials wide industrial application. Major parameters in chemical machining of any material are based on the selection of chemical etchant concentration and its effect on machining outputs. The aim of this study is to examine the effects of selected etchant concentrations and temperatures on depth of etch and surface roughness in chemical machining of copper alloy (copper-zinc alloy - CZ128) with CuCl2. The experimental study was completed in beaker as immerse chemical machining method. The selected etchant concentrations and temperatures were 2.04, 2.33 and 2.65 Mol; and 30°C, 50°C and 70°C. It was concluded that etchant concentration is important parameter on depth of etch, higher etchant concentration increased depth of etch as well as affecting surface quality.

also considered as micromachining method which is widely utilized in micro-electro mechanic system (MEMS) component production [1-10]. The history of chemical machining goes back to Ancient Egypt; copper was etched with citric acid for jewellery production. That means it is the first micromachining process has been employed by human. Later, the process was employed as engraving in the 15th century, mineral acids were used to form complex geometrical shaped and cavities in helmets and breastplates. In 17th century, it was practiced as manufacturing process to shape steel parts. Then, advancement in chemical industry made major development in chemical etching, new etchants and maskants were introduced during 18th-19th centuries [2,5]. The major industrial application has been based on the US patent (US Patent No: 2,739,047); the method was named as “chemical milling” and employed for production aluminum components for rockets and aircrafts [11]. However, the advancement of chemical machining resulted in wider application as machining technique from microelectronics components to medical parts. Chemical machining has several benefits over traditional and nontraditional machining processes such as production of complex geometries with high precision, independent from material’s properties, short machining time and overall low production cost [1-6]. The chemical machining of copper is extensively known in the electronics industry due to influential material properties, but there is very limited information about chemical machining of copper based alloys [12-15]. The selections of chemical machining parameters are based on etchant solution type. The selection of suitable etchant for any material depends on different factors like providing high etch rate and surface finish quality, easy to use and control, cheap and regenerable. Copper based alloys chemically machined with different etchants such as FeCl3, cupric chloride (CuCl2), alkaline etchants (ammonium

INTRODUCTION Chemical machining is a typical nontraditional machining method that implements strong chemical solution to remove unwanted workpiece material by controlled dissolution. The method is extensively applied to produce various sheet components like printed circuit boards, brake rotors, full cell plates, stencils, stamping dies, plaques, signs and printing plates etc. for electronics, precision engineering and medical industries. The machining method is also performed for weight reduction or thinning where using other machining methods would be impossible or too expensive. Chemical machining is 2

Conference Paper

hydroxide and ammonium salts), hydrogen peroxide/sulphuric acid complex and chromic-sulphuric acid solution [7,8]. CuCl2 provides rapid chemical machining. It offers the advantages of easy regeneration. The copper dissolve capacity is also higher, i.e. around 150 g/l in practical applications. It produces no sludge formation. Therefore this etchant seems more economical etchant comparing to other etchants. The present study concentrated on CZ128 copper-zinc alloy with CuCl2 chemical etchant.. Three different etchant solutions and three different etching temperatures were selected. The experimental study was conducted in beaker as immersion etching technique. The study concentrated on the effect of etchant concentration and etching temperature on depth of etch and surface roughness.

were taken from each etched specimen for eliminating misreading.

EXPERIMENTAL PROCEDURE The selected workpiece material was copper-zinc alloy (CZ128). The material is shown as CuZn38Pb2 in EN standard and C37700 in ASTM. The dimension of specimen was 1mmx20mm100mm. The cleaning process was carried out before etching by using firstly acetone and then ultrasonic cleaning technique with prepared solution (mixing of Actoclean pulvar powder with distilled water) at 30°C for 20 mins. The selection of etchant concentration was based on literature review, the chosen etchant concentrations were 2.04 Mol, 2.33 Mol and 2.65 Mol. The etching temperature was selected low (30°C), medium (used in industrial application of copper etching, 50°C) and high (70°C). Etching temperature of 70°C is not industrially applicable, because spray etching machine allows up to 50-55°C. However, it must be noted that the usage of high etching temperature has positive effect on etch rate, but there is no quantitative study in literature. Therefore this paper deals with one of the important output from experimental study determining the influence of high etching temperature on etch rate and surface roughness. The quantity of etchant solution for each experiment was 200 mL. The etchant powder is mixed with distilled water and the solution poured into beaker which was placed into water jacket to stabilize selected etching temperate (±2°C). The experimental set-up of chemical machining was shown in Fig 1. Double sided etching process was conducted and etching was completed after 30 mins etching period, and the measurements were recorded with 5 mins intervals. The outputs of experimental study are thickness of specimen and surface roughness. The thickness was measured by Mitutoyo outside micrometer (deviation was ±0.001) and surface roughness, based on average surface roughness (Ra), was quantified by Taylor-Hobson Surtronic 3+. Three specimens were chemically machined in fresh etchant for each etchant concentration and etching temperature values. Three different measurements of thickness and surface roughness

Fig 1. Chemical machining of CZ128 copper alloy in beaker EXPERIMENTAL RESULTS AND DISCUSSION The chemical reaction of CZ128 copper alloy with CuCl2 as an etchant is shown below: CuCl2 + 0.60 Cu + 0.40 Zn à 1.60 CuCl + 0.40 ZnCl Copper and zinc are oxidized by cupric ions forming CuCl and ZnCl. The experimental study employed three different etchant concentrations for selected material. The effect of these etchant concentrations on depth of etch was shown in Figs 2-4. It was observed that the etchant concentration has positive effect on depth of etch, higher etchant concentration provided higher depth of cut values. After 30 min chemical machining of CZ128 copper alloy, the maximum depth of cut values were 76 µm in 2.65 Mol, 42 µm in 2.33 Mol and 36 µm in 2.04 Mol when 50 °C etching temperature was used. Similar trend could be seen for 30 °C and 70 °C etching temperatures. Etching temperature affects the kinetics of material removal action. It is well known phenomena that medium temperature increases metal corrosion rates. That means application of higher etching temperature would increase etch rate, but there is no qualitative result in literature when this value is more than 50°C. However, it is certain that increased chemical etching temperature, from room temperature to 50°C, produces a higher depth of etch, that means a higher etch rate. The experimental study indicated that, the application of the highest etching temperature would maintain the highest depth of cuts; 60 µm at 30°C, 76 µm at 50 °C and 90 µm at 70°C when 2.65 Mol etchant solution is used. This result 3

Conference Paper

Depth of Etch (µm)

shows that, the chemical machining of any material should be fulfilled as high as possible etching temperature. The lowest etching temperature demonstrated low depth of cuts.

70

Depth of etch (µm)

60 50 40 30

100 90 80 70 60 50 40 30 20 10 0 0

20 10

10

20 Etching time (min)

2.04 Mol

2.33 Mol

30

40

2.65 Mol

0 0

10

20 30 Etching time (min)

2.04 Mol

2.33 Mol

Fig 3. Effect of CuCl2 concentration on depth of etch (Etching temperature : 70°C)

40 2.65 Mol

Surface roughness was experimentally investigated depending on etchant concentration and etching temperature. The surface quality of chemically machined part is significant when thinning of material or weight reduction is required as well as production of micron-sized components. Therefore, the result of surface finish should be determined according to selected parameter in chemical machining of CZ128 copper alloy. The influences of etchant concentrations on surface roughness were presented in Figs 6-8 according to three different etching temperatures. It was noticed that the application of CuCl2 as chemical etchant for selected material produced rougher surface quality. The surface roughness values in lower etchant concentration (2.04 Mol of CuCl2) were slightly better comparing to two other etchant solutions. However, the main parameter in surface roughness was etching temperature; higher etching temperatures produced worst surface finish. The optimum surface roughness value was obtained at 30°C of etching temperature for three etchant solutions. The surface roughness value was around 2µm.

Fig 2. Effect of CuCl2 concentration on depth of etch (Etching temperature: 30°C) 80

Depth of Etch (µm)

70 60 50 40 30 20 10 0 0

10

20

30

40

Etching time (min) 2.04 Mol

2.33 Mol

2.65 Mol

Fig 2. Effect of CuCl2 concentration on depth of etch (Etching temperature: 50°C)

4

Conference Paper

9

Surface roughness (µm)


8 7 6 5 4 3 2 1

0

0 0

10

20

30

30°C

50°C

70°C

9 8 7 6 5 4 3 2 1 0 40

Etching time (min) 30°C

50°C

50°C

70°C

REFERENCES [1] ASM Metals Handbook,1989, (Vol:16: Machining), 9. Edition, ASM Int. Pub., 579-587 [2] T.J. Drozd., C. Wick, 1989, Tool and Manufacturing Engineers Handbook (Chapter 14: Nontraditional Machining), SME Pub., 14-81:15-89 [3] O. Çakır, 2001, “Chemical machining processes”, Proceedings of II. Machine Material and Production Technology Symposium, Turkey, 813-819, (In Turkish) [4] W.T. Harris, 1976, Chemical Milling, Oxford University Press, UK [5] J.W. Dini, 1984, “Fundamentals of chemical milling”, American Machinist (Special Report:768), 113-128 [6] H. McCallion, 1987, “High production chemical milling”, Production Engineer, 66, 14-16 [7] O. Çakır, 2006, “Copper etching with cupric chloride and regeneration of waste etchant”, J. of Materials Processing Technology, 175, 63-68 [8] O. Çakır, 2008, “Review of etchants for copper and its alloys in wet etching processes”, Key Engineering Materials, 364-366, 460-465 [9] D.M. Allen, 1986, The Principles and Practice of Photochemical Machining and Photoetching, Adam Hilger/IOP, UK [10] D.M. Allen, 2015, Photochemical Machining and Photoelectroforming, UK

10

30

40

d. The effect of etchant concentrations on surface roughness showed similar results. e. The impact of etching temperature was clear, low etching temperature produced the best surface finish.

a. The etchant concentration is important parameter, the highest etchant concentration of CuCl2 provided the highest depth of cut. b. The influence of etching temperature is positive on depth of etch. High etching temperatures produced high etch depth for each etchant. This means that the etching temperature increases etch rate.

20

30

Fig 6. Effect of etching temperature on surface roughness (Etchant Concentration : 2.65 Mol)

CONCLUSIONS The following conclusions can be drawn after experimental study of chemical machining of CZ128 copper alloy as follow:

10

20

30°C


0

10

Etching time (min)

40

Etching time (min)


10 9 8 7 6 5 4 3 2 1 0

70°C


5

Conference Paper [11] M.C. Sanz, 1956, “Process of chemically milling structural shapes and resultant article”, US Patent No:2739047, 4 pages, [12] D.M. Allen, O. Çakır, 1994, “Photochemical machining of copper alloys using cupric chloride etchant”, Proceedings of the 6th International Machine Design and Production Conference, (Editors: Ö. Anlağan, F. Arınç, A. Erden, S.E. Kılıç, A.E. Tekkaya), 21-23 September 1994, ODTÜ, Ankara, Turkey, 357-365 [13] D.M. Allen, O. Çakır, H. A.J. White, 1995, “Photochemical machining of brass with cupric chloride etchant and a technique for the partial recovery of dissolved zinc”, Proceedings of the Symposium on High Rate Metal Dissolution Processes, (Editors: M. Data, B.R. MacDoughall, J.M. Fenton), Proceedings Volume: 95-19, (The Electrochemical Society), 8-13 November 1995, Chicago, USA, 305-315 [14] D.M. Allen, O. Çakır, 1996, “The effects of concentration, temperature and HCl additions on the photochemical machining of brass”, Proceedings of the 7th International Machine Design and Production Conference, (Editors: T. Balkan, H. Darendeliler, A. Erden, L. Parnas), 1113 September 1996, ODTÜ, Ankara, Turkey, 191-199 [15] D.M. Allen, O. Çakır, 2002, “Comparison of FeCl3 and CuCl2 in the photochemical machining of brass”, Proceedings of ESDA 2002 (6th Biennial Conference on Engineering Systems Design and Analysis), Istanbul, Turkey, 7 pages

6