Claims:1. A substrate for additive manufacturing wherein the substrate is made of swarf of waste metal chips.

2. The substrate as claimed in claim 1, wherein the metal chips are selected from the group of mild steel, stainless steel, titanium, aluminum and combination thereof.

3. The substrate as claimed in claim 2, wherein the metal chips are made of mild steel.

4. A process of preparation of a substrate for additive manufacturing comprising (i) collecting waste metal chips (swarf) from machining processes; (ii) keeping the same in a hollow die to control spreading and finally (iii) compressing the metal chips (swarf) up to a maximum load of 20 Ton irrespective of the amount of uncompressed swarf in order to form a plate.

5. The process as claimed in claim 4, wherein the metal chips selected from the group of mild steel, stainless steel, titanium, aluminum and combination thereof.

6. The process as claimed in claim 5, wherein the metal chips are made of mild steel.

7. The process as claimed in claim 4, wherein the metal chips (swarf) were compressed using a hydraulic power press (for deep drawing) or a dedicated briquette machine in order to form a plate.

8. The process as claimed in claim 7, wherein the metal chips (swarf) were compressed using a hydraulic power press (for deep drawing) in order to form a plate.

9. A substrate for Wire Arc Additive Manufacturing wherein the substrate is made of swarf of waste metal chips and made by the process claimed in claims 4-8; and wherein the substrate was mounted over a fixture with the help of metal strips to hold tightly the substrate with the platform.

10. A support structure made of compressed swarf manufactured by the process as claimed in claims 4 to 8.
, Description:
TECHNICAL FIELD OF THE INVENTION

The present invention relates to alternate substrates for additive manufacturing, more particularly, a swarf-based substrate for Wire Arc Additive Manufacturing, and a process of preparation of the same.

BACKGROUND OF THE INVENTION

Additive manufacturing is a layer by layer manufacturing process which provides the freedom to design and fabricate the complex parts without worrying about the approach to manufacture. Over the years, the process has seen many developments making it applicable to a wide range of materials and the fields of application. One such process is wire + arc additive manufacturing (WAAM) which incorporates the raw material in wire form, melted by an electric arc and deposited over the required sites. This process is evolved from conventional arc-based welding techniques and has many benefits over its contemporary processes. Weld deposited materials do not exhibit porosity, and their mechanical strength is better as compared to sprayed material and powder-based additive manufacturing processes (Townsend et al. 2016). Weld based Additive manufacturing (WAAM) could manufacture metal parts which are free from stair-step defects common in solid free-form fabrication (Merz et al. 1994). High deposition rates of the process made it possible to fabricate large metal parts (Kazanas et al. 2012; Ward, Fadden, and Quinn 2018).

WAAM uses a metallic solid substrate for part deposition. The substrate needs to be electrically and thermally conductive to complete the electric circuit and dissipate the deposition heat, respectively. Generally, the substrate is a thick metallic plate which can withstand the deformation due to high heat energy and residual stresses. The circular parts such as the propeller could also be deposited on the cylindrical substrate, which later becomes an integral part of the propeller (Ya and Hamilton 2018). However, in many cases, the deposited part needs to be separated from the substrate. Since the weld deposition creates a fusion joint, it becomes challenging to separate the part from the substrate. This difficulty enhances in many folds for large and complex parts. Methods such as using different weld settings and coating (Haselhuhn et al. 2015, 2016) have been used. Controlling the deposition parameter for the first layer to obtain a porous structure could be another possible solution. Though these approaches seem promising; however, it makes the process material-specific or controlling of parameters a real challenge for alloys and different materials. Therefore, a universal solution needs to be developed. Compressed swarf as base-substrate could be used as a solution which requires minimum machining. The proposed solution is very promising as only limited chips would fuse with the part first layer, which can be machined easily to obtain a finished part. Reusing waste swarf would also help in conserving natural resources, environment, economy and energy (Singh, Ramakrishna, and Gupta 2017).

The requirement of machining (also considered as a secondary manufacturing process) has increased significantly with industrial growth and the need for a quality product, causing the loss of a large amount of material in the form of chips/swarf. This waste swarf could be used for other potential applications as suggested by some of the researchers. G Vijayakumar et al. 2012 has utilised the lathe scrap by mixing 1.5 % of it into reinforced concrete, which resulted in 20.25-44% increase in compressive strength and a 33.2% increase in tensile strength. Da Costa, Zapata, and Parucker 2003 recycled grey cast iron chips to use it as a starting material in the powder metallurgy processes. The obtained powder showed good results in terms of consolidation of particles, physical characteristics and similarity to industrial furnace powders. Karadag, Bahtli, and Kara 2016, attempted to convert brass and steel chips into a finished product by compression. The compression was followed by hardness (Brinell test) and three-point bending test to assure the quality. They found that the mechanical properties of produced composite were comparable to cast brass. Fullenwider et al. 2019 produced stainless steel powder by the recycling of machining chips using ball milling. The machining chips were successfully converted into near-sphere shaped powder particles with size ranging from 38 µm to 150 µm. The powder was further utilised in the laser engineered net shaping (LENS) process to make metal parts. Chmura and Gronostajski 2007 recycled aluminium and aluminium-alloy chips by direct conversion method that includes granulation and cleaning, cold compaction, hot extrusion and heat treatment. The process created hard load-carrying particles inside a soft aluminum layer. They found the particles were ideal for bearing materials. Azis et al. 2015 applied a purification process onto a steel waste to prepare ferrites. High purity hematite (Fe2O3) was yielded as confirmed by X-ray diffraction (XRD), X-ray Fluorescence (XRF) and Energy-dispersive X-ray Spectroscopy (EDAX). Namit et al. 2018 used waste metal chips in welding in place of traditional filler material to fill the butt joint. They obtained sufficient penetration of the weld joint without blow holes and 2.5 times more hardness of the weld zone as compared to the base metal.

The above literature shows the potential of waste metal chips into various unique applications. WAAM is an arc-welding based process to manufacture three-dimensional parts. The deposition requires a heavy metallic substrate/ plate considering the requirement of electrical and thermal conductivity to complete the electric circuit and ensure the heat dissipation, respectively. Also, a heavy substrate is less prone to deform due to heat. However, it becomes difficult to separate the deposited part from the substrate. The part needs to be separated by machining, e.g. using an angle grinder, which causes a loss of significant material. This difficulty in separation enhances in many folds for large and complex parts. Significant machining is also required to reuse the substrate again.

No patent was found addressing a similar issue as this invention; however, some patents related to the sub-processes are mentioned below.

Hassel et al. (US 2018/0133804 A1) invented a process to use the recycled alloys chips for making metal components. They formed metal alloy powder after cleaning, melting, removal of the impurities, deoxidising the melt, and then atomising the metal chips. They claimed that the cost was reduced by utilising the obtained powder for the fabrication of metal components such as brackets, fuel injectors, lubricating nozzles, etc.

Cam Borne Industries PLC (International publication number: WO 1992/01073) presented a process for the recycling of metal swarf by compacting, heating and then cooling it in a non-oxidising environment. The formed billet had a density of about 85% of the solid metal and was machined to a finished or semi-finished product.

Prinz et al. (EP 1993/0529816) patented the use of a CNC machine for additive manufacturing using a welding head. Milling tools were used after every layer of deposition to make the surface plane for next layer deposition. It also included a head that supplied complementary material (powder) to support the growing object for overhanging features. It could be later removed by chemical etching or machining.

Braun et al. (US 1993/5233150) developed a control system to properly deposit material in an additive manufacturing process using gas metal arc welding (GMAW) as a deposition head. It sensed the discontinuities in welding current or voltage and adjusted the parameters to make it smoother in the next layer. They also developed a tool path planning which first deposits the outline of the layer then fills it.

Wright et al. (US 2003/189082) presented a process to provide support in weld based additive manufacturing processes. The substrate was tilted, and the welding head was kept vertical to make an inclined part.

Jones et al. (US 2002/139779) presented part forming (WAAM) by using a modified foundation (substrate), instead of depositing over a conventional plane substrate. A raised part is used to deposit the body as per the part base or first layer geometry. The raised part can have many variations, and the deposition head could be manipulated with respect to the foundation to deposit the body.

Though no related patent was found, the problem was attempted by a few researchers (Haselhuhn, Wijnen, Anzalone, Sanders, & Pearce, 2015) by using different approaches. These approaches are using thin coatings over the substrate and modification in deposition parameters to promote weaker joints between part and substrate, which could help to remove the deposited part.

However, present invention provides a novel approach to solve the above mentioned problems by offering an alternate substrate to be used that is capable to address all the issues as mentioned above.

SUMMARY OF THE INVENTION

The following disclosure presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.

The main object of present invention is to provide an alternate substrate to be used in additive manufacturing which is useful as the deposited parts can be easily removed from the substrate due to the porous nature of it and require minimal machining to remove fused chips. The present invention would also be beneficial for making collapsible support structures required for overhang deposition. Moreover, it involves the reuse of waste metal chips which in turn would help the environment and also reduces the cost of production.

One aspect of present invention relates to a substrate for additive manufacturing wherein the substrate is made of swarf of waste metal chips.

Another aspect relates to a process of preparation of a substrate for additive manufacturing comprising (i) collecting waste metal chips (swarf) from machining processes; (ii) keeping the same in a hollow die to control spreading and finally (iii) compressing the metal chips (swarf) up to a maximum load of 20 Ton irrespective of the amount of uncompressed swarf in order to form a plate.

Yet another aspect relates to a substrate for Wire Arc Additive Manufacturing wherein the substrate is made of swarf of waste metal chips and made by the process disclosed above; and wherein the substrate was mounted over a fixture with the help of metal strips to hold tightly the substrate with the platform.

Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The above and other aspects, features and advantages of the embodiments of the present disclosure will be more apparent in the following description taken in conjunction with the accompanying drawings, in which:

Figure 1 illustrates sample substrate made by compressing metal swarf as disclosed in one of the embodiment of present invention. The figure shows the metal chips that were used for making the substrate (left). It also shows the substrate compressed into a cylindrical disk (right).

Figure 2 illustrates the swarf-based substrate (top-view) mounted over a fixture through clamps as disclosed in one of the embodiment of present invention. The figure shows the top view of the substrate mounted over a typical fixture. Four clamps were used for holding the substrate. In this figure, only the substrate is the part of invention.

Figure 3 illustrates front view of a layer being deposited over the swarf-substrate (side-view) in a representative wire arc additive manufacturing setup as disclosed in one of the embodiment of present invention.

Figure 4 illustrates a straight wall of length 70 mm and height 16 mm obtained by 10 layers of deposition as disclosed in one of the embodiment of present invention.

Figure 5 illustrates a hollow square pipe from the deposition of the substrate to machining, (a) as-deposited, (b) after separating from the substrate, and (c) after machining the chips as disclosed in one of the embodiment of present invention.

Figure 6 illustrates a decorative item (a) as-deposited (b) after finishing as disclosed in one of the embodiment of present invention.

Figure 7 illustrates (a) CAD model of an approach to deposit overhanging features using the swarf-based substrate, (b) part demonstrating the use of swarf substrate as support structure, (c) after separating from the substrate, and (d) after machining the chips, bottom view (left) and top view (right) as disclosed in one of the embodiment of present invention.

Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may not have been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure. Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of various embodiments of the present disclosure as defined by the claims and their equivalents. It includes various specific details to assist in that understanding, but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the various embodiments described herein can be made without departing from the scope and spirit of the present disclosure. In addition, descriptions of well-known functions and constructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the present disclosure. Accordingly, it should be apparent to those skilled in the art that the following description of various embodiments of the present disclosure is provided for illustration purpose only and not for the purpose of limiting the present disclosure as defined by the appended claims and their equivalents.

It is to be understood that the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, a reference to "a component surface" includes a reference to one or more of such surfaces.

All terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which various embodiments belong. Further, the meaning of terms or words used in the specification and the claims should not be limited to the literal or commonly employed sense but should be construed in accordance with the spirit of the disclosure to most properly describe the present disclosure.

The terminology used herein is for the purpose of describing particular various embodiments only and is not intended to be limiting of various embodiments. As used herein, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising" used herein specify the presence of stated features, integers, steps, operations, members, components, and/or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, members, components, and/or groups thereof. Also, expressions such as "at least one of," when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list.

The present disclosure will now be described more fully with reference to the accompanying drawings, in which various embodiments of the present disclosure are shown. The present disclosure may, however, be embodied in many different forms and should not be construed as being limited to the various embodiments set forth herein, rather, these various embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the present disclosure. Furthermore, a detailed description of other parts will not be provided not to make the present disclosure unclear. Like reference numerals in the drawings refer to like elements throughout.

The present invention relates to a substrate for additive manufacturing wherein the substrate is made of swarf of waste metal chips.

In a preferred embodiment the metal chips are selected from the group of mild steel, stainless steel, titanium, aluminum and combination thereof.

In a most preferred embodiment the metal chips are made of mild steel.

In another embodiment of present invention relates to a process of preparation of a substrate for additive manufacturing comprising (i) collecting waste metal chips (swarf) from machining processes; (ii) keeping the same in a hollow die to control spreading and finally (iii) compressing the metal chips (swarf) up to a maximum load of 20 Ton irrespective of the amount of uncompressed swarf in order to form a plate.

In a preferred embodiment the metal chips are selected from the group of mild steel, stainless steel, titanium, aluminum and combination thereof.

In a most preferred embodiment the metal chips are made of mild steel.

In a preferred embodiment the metal chips (swarf) were compressed using a hydraulic power press (for deep drawing) or a dedicated briquette machine in order to form a plate.

In a most preferred embodiment, the metal chips (swarf) were compressed using a hydraulic power press (for deep drawing) in order to form a plate.

Yet another aspect relates to a substrate for Wire Arc Additive Manufacturing wherein the substrate is made of swarf of waste metal chips and made by the process disclosed above; and wherein the substrate was mounted over a fixture with the help of metal strips to hold tightly the substrate with the platform.

Examples

A collapsible substrate for WAAM application was made by compressing the swarf (Fig 1). It consisted of waste metal chips of mild steel from various machining operations, particularly turning and facing. It was compressed using a hydraulic power press (for deep drawing) in order to form a plate. The machine compressed the swarf up to a maximum load of 20 Ton irrespective of the amount of uncompressed swarf. This feature helped in achieving the identical substrate density for different thickness. Hence, the different thickness of the compressed swarf can be obtained by taking the known weight quantity (in kg) of the swarf. It was compressed inside a hollow circular die of 140 mm inner diameter and height of 80 mm to control the spreading. The dimension of the die and punch could also be chosen depending on the requirement of the substrate. A 160 gms of swarf was used to make a substrate of thickness 3 mm and diameter 140 mm. The substrate had a density of ?3.5 g/cm3, which is ?44% of the solid- mild steel. Though the thickness, shape, load which in turn will determine the density can be varied depending on the requirement.

The swarf-substrate was mounted over a fixture with the help of metal strips (Fig. 2). The metal strips helped the swarf-substrate to hold tightly with the platform. The area between the metal strips is the useful area of the swarf-substrate for deposition purposes.

This compressed swarf-based substrate was used by WAAM to deposit different geometries and analyse its effectiveness for the purpose. Fig. 3 shows the WAAM setup where the platform was movable in X-Y directions. A deposition head which was basically a welding torch was used for the deposition and was movable in Z direction. A part layer is being deposited over the swarf-substrate. The deposition head was powered by a gas metal arc welding machine which controls the deposition parameters. The motion of platform along X-Y direction and deposition head along Z direction was controlled and programmed by a computer. The platform was electrically conductive and connected to the negative terminal of the gas metal arc welding machine.

Fig. 3 shows the substrate use in the WAAM process. The substrate is mounted over the platform which can move in XY direction. A deposition torch is located over the substrate and can move in Z direction. An electric arc is formed between the substrate and the feed wire which melts the wire and deposit it over the substrate. Here the substrate is the proposed invention, and the other art shows the general arrangement of WAAM process.

Fig. 4 shows a straight wall of length 70 mm and height 16 mm obtained by 10 layers of deposition. The deposition was performed with optimised parameters for gas metal arc welding (GMAW), i.e. input voltage 16 V, wire feed rate 3.5 m/min and deposition speed 300 mm/min. It was observed that increasing the input power led to severe melting of the substrate and formation of the melt hole. Further, it was observed for the first deposited layer, the bead had low height and high width as compared to solid substrate. The deposited metal spread over the substrate up to a width of 8-10 mm, seeped inside the pores substrate and melted the surrounding/affected chips. At lower power inputs, a discontinuous bead was observed. After deposition, this low-density substrate was broken easily, leaving the deposited part with a few fused chips at the bottom.

Fig. 5 demonstrates the deposition of hollow square part on compressed swarf substrate. The part consists of 15 layers to achieve a height of about 20 mm. Fig. 5b shows the typical example where the fused chips could be seen at the bottom of the part. The figure also demonstrates that unlike the solid substrate, the removal of chips from the hollow portion was much easier with the proposed method. Fig. 5c shows a finished product after machining.

Fig. 6 shows another part of geometry deposited by WAAM to demonstrate the process capability. It can be seen that the substrate only affects the bottom layer of the part, and the rest of the layers are not affected by the substrate. The part was also machined to reveal the cross-section (Fig. 6b).

Support structures are often required in additive manufacturing for supporting the overhanging part. Fig. 7a shows a representative geometry where the proposed method has an added advantage to promote the support structure. It consists of two cylinders of different diameters with a step transition. These cylinders were joined together with the help of six-spokes. The figure shows the design complexity involved in depositing the part, as the spokes are overhanging, and ends are only joining the two parts. Here, the part was deposited by first depositing the larger cylinder on a swarf substrate. After that, the cylinder was again filled with the chips and compressed to make a substrate for further deposition. Then, the spokes and the smaller cylinder were deposited. Since the swarf substrate is easily destroyable, the spokes were separated without any difficulty.

These types of geometrical features bring a great challenge to welding based additive manufacturing processes which would not have been possible without the use of support structures. Further, removal of swarf-based substrate and/ or supports are much easier as compared to solid supports. It reduced the post machining process significantly without damaging the thin spokes. The possible applications of this type of structure could be employed in components such as alloy wheels.

The inventiveness of the proposed method is that the swarf can be converted into a substrate which can be utilised for WAAM. The compressed metal swarf provides sufficient strength to serve the purpose of the substrate. Due to its porous nature, it is easily collapsible, which is suitable for the requirement that ‘the deposited part should be easily removable’. It could also fulfil the requirement of the support structure wherever needed.

The electrically and thermally conductive nature of the metal swarf brings no limitation to the WAAM process. The present invention is demonstrated only for WAAM; however, it could also be used for other additive manufacturing processes such as laser engineered net shaping (LENS), selective laser sintering (SLS), direct metal deposition (DMD), etc.

The features and benefits of this invention are:
a) The substrate is made of waste metal chips which helps in the recycling of machining wastes.
b) It could also be used as a support material, as demonstrated in fig. 7.
c) It is easily collapsible.
d) No specific parameters are required for the first layer deposition.
e) The swarf-based substrate is easy to handle as compared to the conventional substrate.
f) Less machining is required to remove the fused swarf from the base. Low machining forces would also protect thin geometries (if any).